The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 94, Issue 2

Scientific Articles | January 18, 2012

Development of Knee Function After Hamstring Lengthening as a Part of Multilevel Surgery in Children with Spastic Diplegia: A Long-Term Outcome Study

Thomas Dreher, MD¹; Dóra Vegvari, MD¹; Sebastian I. Wolf, PhD¹; Andreas Geisbüsch, MD¹; Simone Gantz, MSc¹; Wolfram Wenz, MD¹; Frank Braatz, MD¹

¹ Department of Orthopaedic and Trauma Surgery, Heidelberg University Clinics, Schlierbacher Landstrasse 200a, 69118 Heidelberg, Germany. E-mail address for T. Dreher: thomas.dreher@med.uni-heidelberg.de

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Investigation performed at the Department of Orthopaedic and Trauma Surgery, Heidelberg University Clinics, Heidelberg, Germany

Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

J Bone Joint Surg Am, 2012 Jan 18;94(2):121-130. doi: 10.2106/JBJS.J.00890

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Abstract

Background:

Hamstring lengthening commonly is performed for the treatment of flexed knee gait in patients with spastic diplegic cerebral palsy. Satisfactory short-term results after hamstring lengthening have been demonstrated in various studies. However, evidence for the effectiveness of hamstring lengthening to correct flexed knee gait is scant because of small and inhomogeneous case series, different surgical techniques, and short follow-up.

Methods:

The long-term results for thirty-nine patients with spastic diplegia and flexed knee gait who were managed with intramuscular hamstring lengthening as a part of multilevel surgery are presented. Standardized three-dimensional gait analyses and clinical examinations were performed for all patients preoperatively and at one, three, and six to twelve years postoperatively.

Results:

Significant improvements in kinematic parameters and the popliteal angle were noted at short-term follow-up (p < 0.01), supporting the results of previous studies. Long-term results showed significant deterioration of minimum knee flexion in stance and the popliteal angle (p < 0.01), whereas the improvements in the Gross Motor Function Classification System and Gillette Gait Index were maintained. This recurrence of flexed knee gait is partial and measurable. Increased pelvic tilt was found in 49% of the limbs postoperatively, which may represent one factor leading to recurrence of flexed knee gait. Genu recurvatum was seen in eighteen patients (twenty-seven limbs; 35%) one year postoperatively, especially in the patients with a jump knee gait pattern preoperatively. At long-term follow-up, genu recurvatum resolved in many limbs, but 12% of the limbs showed residual genu recurvatum, indicating that overcorrection represents a problem following hamstring lengthening.

Conclusions:

The results of the present study are crucial for the prognosis of knee function after hamstring lengthening as a part of multilevel surgery. Recurrence and possible overcorrection should be considered in treatment planning.

Level of Evidence:

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | Acknowledgements

Ambulatory children with spastic diplegic cerebral palsy and gait disturbances commonly are managed with single-event multilevel surgery, which combines different osseous and soft-tissue procedures to achieve correction in all planes and on all levels^1-7. Increased knee flexion during the stance phase of gait (flexed knee gait) is one of the most common gait abnormalities in spastic diplegia⁸. Rodda et al. further classified flexed knee gait into four patterns⁹: true equinus, jump knee, apparent equinus, and crouch. Hamstring spasticity with resultant contracture has been identified as one of the main factors leading to a flexed knee gait^8,10-15. Later investigations have shown that increased external tibial torsion, instability of the foot, and quadriceps weakness can cause or aggravate flexed knee gait^16-20. Lengthening of the hamstrings is widely considered to be the standard surgical procedure for the correction of increased knee flexion^21-25. The hamstrings can be lengthened with use of an open or a percutaneous technique^24,26-28. Satisfactory short-term results with improved knee extension during stance phase have been shown in different studies^22,24,27,29. However, outcomes have been inconsistent; many patients have had improvement, whereas other patients have had only little benefit or even worsening^24,26-30. After short-term follow-up, some authors have reported increased pelvic tilt and a high prevalence of genu recurvatum as a consequence of overcorrection^23,24,27. Evidence for the effectiveness of hamstring lengthening to correct flexed knee gait in spastic diplegia is scant because of small and inhomogeneous case series, different surgical techniques, and short follow-up. As a result, hamstring lengthening currently is viewed as controversial. A major problem is that, to our knowledge, there have been no long-term studies investigating the effects of hamstring lengthening in skeletally mature patients who were managed in childhood. Therefore, the long-term results in adolescents and adults who had had hamstring lengthening as a part of multilevel surgery in childhood were investigated in the present study. Our hypothesis was that correction of flexed knee gait seen at short-term follow-up is not maintained in the long term.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | Acknowledgements

Standardized three-dimensional gait analysis and clinical examination were routinely performed for all ambulatory patients with cerebral palsy before and after surgery at our institution. Regular follow-up examinations were planned for each patient.

For the present study, all ambulatory diplegic patients with flexed knee gait who were managed with hamstring lengthening as part of multilevel surgery in childhood between 1996 and 2003 were selected from the gait laboratory database. One hundred and fifty-five patients were identified. For inclusion in the present study, the patients had to have undergone at least two standardized postoperative examinations (three-dimensional gait analysis and clinical examination) at one year and at two to four years after surgery. Ninety-four patients matched these criteria. All ninety-four patients were scanned for exclusion criteria and afterward were reinvited for a third long-term follow-up examination at least six years after surgery. The exclusion criteria were previous orthopaedic surgery (eight patients), dyskinetic cerebral palsy (five patients), botulinum-toxin-A injections in the six months prior to single-event multilevel surgery (five patients), severe mental retardation (three patients), and loss of walking ability (two patients). Three patients who had had revision surgery for hamstring lengthening or other secondary procedures between the examinations, which potentially may have influenced the results, were also excluded from the present study. After the exclusion of patients, sixty-eight patients remained eligible for reevaluation. Thirty-nine patients who had had a mean age (and standard deviation) of 10.3 ± 3.5 years (range, six to sixteen years) at the time of surgery could be reevaluated and were included in the present study. Subjects and/or families or caretakers gave informed consent to participate in the present study, which was approved by an institutional ethics committee.

Static findings, including knee range of motion and the popliteal angle³¹, and dynamic findings, obtained by means of conventional, instrumented, three-dimensional gait analysis³², were evaluated four times: preoperatively (E0) and at one year (E1), two to four years (E2), and six to twelve years (E3) postoperatively. Demographic data, the results of Gross Motor Function Classification System testing^33,34, and baseline sagittal pattern⁹ distribution are displayed in Table I.

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TABLE I Demographic Data and Functional Baseline Parameters*†

Parameter	E0	E1	E2	E3
Time of follow-up‡(yr)		1.0 ± 0.2	3.1 ± 1.0	8.1 ± 1.8
Age‡(yr)	10.2 ± 3.5	11.3 ± 3.5	13.5 ± 3.3	18.5 ± 4.5
Gross Motor Function Classification System (no. of patients)
Level I	6	11	14	13
Level II	21	11	16	13
Level III	12	17	9	13
Preoperative sagittal gait pattern§(no. of limbs)
Group I (true equinus)	0
Group II (jump knee)	33
Group III (apparent equinus)	12
Group IV (crouch)	33

*There were thirteen female patients and twenty-six male patients in the present study.
†E0 = preoperatively, E1 = one year postoperatively, E2 = two to four years (mean, three years) postoperatively, and E3 = six to twelve years (mean, eight years) postoperatively.
‡The values are given as the mean and the standard deviation.
§Sagittal gait pattern classification according to the system of Rodda et al.⁹, obtained from preoperative, instrumented, three-dimensional gait analysis.

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TABLE I Demographic Data and Functional Baseline Parameters*†

Parameter	E0	E1	E2	E3
Time of follow-up‡(yr)		1.0 ± 0.2	3.1 ± 1.0	8.1 ± 1.8
Age‡(yr)	10.2 ± 3.5	11.3 ± 3.5	13.5 ± 3.3	18.5 ± 4.5
Gross Motor Function Classification System (no. of patients)
Level I	6	11	14	13
Level II	21	11	16	13
Level III	12	17	9	13
Preoperative sagittal gait pattern§(no. of limbs)
Group I (true equinus)	0
Group II (jump knee)	33
Group III (apparent equinus)	12
Group IV (crouch)	33

Hamstring lengthening was considered for patients who had increased knee flexion at initial contact (at least 20°) and/or in midstance (at least 10°) as observed with three-dimensional gait analysis in combination with at least 30° of knee extension deficiency on the popliteal angle test and/or any knee contracture.

All patients underwent standardized single-event multilevel surgery, including osseous and soft-tissue procedures (Table II). The intraoperative goal of hamstring lengthening for the correction was to achieve a popliteal angle of 20°. Medial hamstring lengthening was done first, through a 3 to 4-cm medial incision at the transition between the proximal and the distal half of the thigh, about 7 to 12 cm above the popliteal crease with the patient in the supine position. Fractional lengthening of the semimembranosus muscle was achieved by means of transverse incisions in the aponeurosis (aponeurotic lengthening) at a single level or at several levels if needed. The semitendinosus muscle was lengthened by means of intramuscular tenotomy on the same level through the same approach. The gracilis tendon frequently was used for distal rectus femoris transfer. If the correction was still insufficient (>20° on the popliteal angle test) after medial hamstring lengthening, the biceps femoris muscle was lengthened with use of a fractional intramuscular aponeurotic lengthening technique at the distal dorsolateral part of the thigh.

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TABLE II Number of Surgical Procedures Performed in Single-Event Multilevel Surgery*

Procedure	All (N = 78)	Medial Hamstring Lengthening Group (N = 60)	Combined Medial and Lateral Hamstring Lengthening Group (N = 18)
Medial hamstring lengthening	78	60	18
Lateral hamstring lengthening	18	0	18
Psoas over the brim	14	7	7
Proximal rectus femoris recession	36	30	6
Adductor longus recession	10	7	3
Distal rectus femoris transfer	71	56	15
Calf muscle lengthening	54	45	9
Soft-tissue procedures, foot (split or complete posterior tibial tendon transfer, split anterior tibial tendon transfer)	18	14	4
Femoral derotation osteotomy	48	38	10
Tibial derotation osteotomy	5	2	3
Osseous foot stabilization (Evans calcaneal lengthening osteotomy; Grice extra-articular subtalar arthrodesis; Chopart or triple arthrodesis; calcaneocuboid joint distraction arthrodesis)	41	31	10

*The values are given as the number of limbs.

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TABLE II Number of Surgical Procedures Performed in Single-Event Multilevel Surgery*

Procedure	All (N = 78)	Medial Hamstring Lengthening Group (N = 60)	Combined Medial and Lateral Hamstring Lengthening Group (N = 18)
Medial hamstring lengthening	78	60	18
Lateral hamstring lengthening	18	0	18
Psoas over the brim	14	7	7
Proximal rectus femoris recession	36	30	6
Adductor longus recession	10	7	3
Distal rectus femoris transfer	71	56	15
Calf muscle lengthening	54	45	9
Soft-tissue procedures, foot (split or complete posterior tibial tendon transfer, split anterior tibial tendon transfer)	18	14	4
Femoral derotation osteotomy	48	38	10
Tibial derotation osteotomy	5	2	3
Osseous foot stabilization (Evans calcaneal lengthening osteotomy; Grice extra-articular subtalar arthrodesis; Chopart or triple arthrodesis; calcaneocuboid joint distraction arthrodesis)	41	31	10

*The values are given as the number of limbs.

Postoperative management consisted of early mobilization with immediate weight-bearing. Epidural analgesia was used to manage postoperative pain during mobilization. In patients with additional osseous procedures, weight-bearing was done three to four weeks after surgery. In cases with residual knee contracture, controlled serial thigh casting was used postoperatively to achieve full knee extension within five to seven days. All patients were fitted with thigh night splints for six months to maintain knee extension.

To further describe the type of flexed knee gait, the patterns were classified for all patients according to the system of Rodda et al.⁹ (Table I).

Significant correlations between the parameters of the left and right limbs were found (p < 0.05). Due to this dependence, data analysis was done only for the left limbs of the patients in selected parameters from the clinical examination and three-dimensional gait analysis. Furthermore, subgroup analysis was performed for the medial hamstring lengthening and combined medial and lateral hamstring lengthening groups. Descriptive statistics were used for basic statistical analysis. To show time-changing effects, one-way repeated-measures analyses of variance were applied. To assess significant changes in the prevalence of adverse effects (genu recurvatum, increased pelvic tilt) at the three different postsurgical examinations, the McNemar test was applied. The level of significance was set at p < 0.05, and the Bonferroni correction was employed to adjust for multiple comparisons. Statistical analysis was performed with use of PASW Statistics 18 (SPSS, Chicago, Illinois).

Source of Funding

No external source of funding was used for this investigation.

Results

Introduction | Materials and Methods | Results | Discussion | Acknowledgements

Clinical Examination and Walking Ability

The total number of independent walkers did not change over the years, whereas the Gross Motor Function Classification System levels improved, with seven more patients showing Gross Motor Function Classification System level I at E3 in comparison with E0 (Table I). No significant differences were observed in the Gross Motor Function Classification System level between the medial hamstring lengthening and the combined medial and lateral hamstring lengthening groups at baseline (E0).

A significant reduction in the mean popliteal angle was noted at E1 (Table III, Fig. 1). Between E1 and E3, all patients had significant deterioration of the popliteal angle. The popliteal angle deteriorated mainly between E2 and E3 in both groups. At E3, the popliteal angle was not significantly different from the preoperative values in either group.

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TABLE III Mean Values and Statistical Results for Selected Parameters*†‡

Parameter	E0	E1	E2	E3
Popliteal angle (deg)
All	51 ± 18#**	30 ± 19§††	38 ± 16§††	49 ± 16#**
Medial hamstring lengthening	47 ± 17#	28 ± 19§††	37 ± 15††	51 ± 15#**
Combined medial and lateral hamstring lengthening	66 ± 11#	38 ± 17§	43 ± 19	43 ± 21
Speed (m/s)
All	0.82 ± 0.23#	0.70 ± 0.32§**††	0.87 ± 0.30#	0.92 ± 0.30#
Medial hamstring lengthening	0.83 ± 0.23#††	0.70 ± 0.30§**††	0.88 ± 0.28	0.96 ± 0.28#
Combined medial and lateral hamstring lengthening	0.78 ± 0.21	0.71 ± 0.41	0.84 ± 0.37	0.79 ± 0.35
Cadence (steps/min)
All	120 ± 24#	100 ± 30§**††	113 ± 26	119 ± 21
Medial hamstring lengthening	123 ± 26#	104 ± 27§	115 ± 25	114 ± 20
Combined medial and lateral hamstring lengthening	113 ± 13	88 ± 37	104 ± 27	104 ± 23
Stride length (m)
All	0.82 ± 0.19**††	0.82 ± 0.24**††	0.91 ± 0.23§#	0.97 ± 0.21§#
Medial hamstring lengthening	0.82 ± 0.21††	0.79 ± 0.23**††	0.90 ± 0.23#††	0.99 ± 0.20§#**
Combined medial and lateral hamstring lengthening	0.82 ± 0.12	0.91 ± 0.23	0.95 ± 0.26	0.89 ± 0.24
Gillette Gait Index
All	378 ± 240#**††	225 ± 172§	207 ± 168§	217 ± 134§
Medial hamstring lengthening	377 ± 267#**††	207 ± 142§	201 ± 177§	208 ± 130§
Combined medial and lateral hamstring lengthening	380 ± 129**	287 ± 249	228 ± 139§	246 ± 149
Mean pelvic tilt (deg)
All	17 ± 9	21 ± 8**	17 ± 8#	18 ± 8
Medial hamstring lengthening	17 ± 8	20 ± 7**	17 ± 8#	18 ± 7
Combined medial and lateral hamstring lengthening	16 ± 10	22 ± 10	17 ± 10	20 ± 10
Knee flexion at initial contact (deg)
All	38 ± 17#**††	17 ± 11§**††	22 ± 11§#	23 ± 10§#
Medial hamstring lengthening	36 ± 17#**††	16 ± 12§**††	22 ± 11§#	23 ± 10§#
Combined medial and lateral hamstring lengthening	45 ± 14#**††	19 ± 8§	20 ± 12§	23 ± 10§
Mean knee flexion in stance (deg)
All	30 ± 19#**††	11 ± 12§**††	18 ± 13§#	20 ± 11§#
Medial hamstring lengthening	27 ± 18#**	10 ± 13§**††	17 ± 12§#	20 ± 11#
Combined medial and lateral hamstring lengthening	42 ± 20#††	15 ± 12§	20 ± 16	21 ± 14§
Minimum knee flexion in stance (deg)
All	21 ± 22#**††	1 ± 14§**††	10 ± 13§#	12 ± 13§#
Medial hamstring lengthening	17 ± 20#**	0 ± 14§**††	9 ± 12§#	12 ± 12#
Combined medial and lateral hamstring lengthening	35 ± 23#††	7 ± 12§	12 ± 16	12 ± 16§
Maximum internal knee flexor moment (Nm/kg*m)	0.55 ± 0.27	0.40 ± 0.21	0.52 ± 0.27	0.55 ± 0.24
Maximum internal knee extensor moment (Nm/kg*m)	−0.37 ± 0.25	−0.47 ± 0.29	−0.42 ± 0.22	−0.50 ± 0.31

*The values are given as the mean and the standard deviation. The study included thirty-nine patients overall, with thirty patients in the isolated medial hamstring lengthening group and nine in the combined medial and lateral hamstring lengthening group. All outcome parameters were evaluated for all thirty-nine patients, with the exception of maximum internal knee flexor and extensor moment (which was evaluated for nineteen patients).
†Significance was determined with repeated measures of analysis of variance with Bonferroni correction. The level of significance was set at p < 0.05.
‡E0 = preoperatively, E1 = one year postoperatively, E2 = two to four years (mean, three years) postoperatively, and E3 = six to twelve years (mean, eight years) postoperatively.
§Significantly different from E0.
#Significantly different from E1.
**Significantly different from E2.
††Significantly different from E3.

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TABLE III Mean Values and Statistical Results for Selected Parameters*†‡

Parameter	E0	E1	E2	E3
Popliteal angle (deg)
All	51 ± 18#**	30 ± 19§††	38 ± 16§††	49 ± 16#**
Medial hamstring lengthening	47 ± 17#	28 ± 19§††	37 ± 15††	51 ± 15#**
Combined medial and lateral hamstring lengthening	66 ± 11#	38 ± 17§	43 ± 19	43 ± 21
Speed (m/s)
All	0.82 ± 0.23#	0.70 ± 0.32§**††	0.87 ± 0.30#	0.92 ± 0.30#
Medial hamstring lengthening	0.83 ± 0.23#††	0.70 ± 0.30§**††	0.88 ± 0.28	0.96 ± 0.28#
Combined medial and lateral hamstring lengthening	0.78 ± 0.21	0.71 ± 0.41	0.84 ± 0.37	0.79 ± 0.35
Cadence (steps/min)
All	120 ± 24#	100 ± 30§**††	113 ± 26	119 ± 21
Medial hamstring lengthening	123 ± 26#	104 ± 27§	115 ± 25	114 ± 20
Combined medial and lateral hamstring lengthening	113 ± 13	88 ± 37	104 ± 27	104 ± 23
Stride length (m)
All	0.82 ± 0.19**††	0.82 ± 0.24**††	0.91 ± 0.23§#	0.97 ± 0.21§#
Medial hamstring lengthening	0.82 ± 0.21††	0.79 ± 0.23**††	0.90 ± 0.23#††	0.99 ± 0.20§#**
Combined medial and lateral hamstring lengthening	0.82 ± 0.12	0.91 ± 0.23	0.95 ± 0.26	0.89 ± 0.24
Gillette Gait Index
All	378 ± 240#**††	225 ± 172§	207 ± 168§	217 ± 134§
Medial hamstring lengthening	377 ± 267#**††	207 ± 142§	201 ± 177§	208 ± 130§
Combined medial and lateral hamstring lengthening	380 ± 129**	287 ± 249	228 ± 139§	246 ± 149
Mean pelvic tilt (deg)
All	17 ± 9	21 ± 8**	17 ± 8#	18 ± 8
Medial hamstring lengthening	17 ± 8	20 ± 7**	17 ± 8#	18 ± 7
Combined medial and lateral hamstring lengthening	16 ± 10	22 ± 10	17 ± 10	20 ± 10
Knee flexion at initial contact (deg)
All	38 ± 17#**††	17 ± 11§**††	22 ± 11§#	23 ± 10§#
Medial hamstring lengthening	36 ± 17#**††	16 ± 12§**††	22 ± 11§#	23 ± 10§#
Combined medial and lateral hamstring lengthening	45 ± 14#**††	19 ± 8§	20 ± 12§	23 ± 10§
Mean knee flexion in stance (deg)
All	30 ± 19#**††	11 ± 12§**††	18 ± 13§#	20 ± 11§#
Medial hamstring lengthening	27 ± 18#**	10 ± 13§**††	17 ± 12§#	20 ± 11#
Combined medial and lateral hamstring lengthening	42 ± 20#††	15 ± 12§	20 ± 16	21 ± 14§
Minimum knee flexion in stance (deg)
All	21 ± 22#**††	1 ± 14§**††	10 ± 13§#	12 ± 13§#
Medial hamstring lengthening	17 ± 20#**	0 ± 14§**††	9 ± 12§#	12 ± 12#
Combined medial and lateral hamstring lengthening	35 ± 23#††	7 ± 12§	12 ± 16	12 ± 16§
Maximum internal knee flexor moment (Nm/kg*m)	0.55 ± 0.27	0.40 ± 0.21	0.52 ± 0.27	0.55 ± 0.24
Maximum internal knee extensor moment (Nm/kg*m)	−0.37 ± 0.25	−0.47 ± 0.29	−0.42 ± 0.22	−0.50 ± 0.31

Fig. 1

Histogram showing the development of the popliteal angle (given as the mean and the standard deviation) at E0 (preoperatively), E1 (one year postoperatively), E2 (two to four years [mean, three years] postoperatively), and E3 (six to twelve years [mean, eight years] postoperatively) for all patients (n = 39), for the medial hamstring lengthening (MHL) group (n = 30 patients), and the combined medial and lateral hamstring lengthening (CHL) group (n = 9 patients). Positive values indicate knee flexion.*Significant difference between E0 and E1 (p < 0.001). #Significant difference between E1 and E2 (p < 0.01). ‡Significant difference between E2 and E3 (p < 0.01). n.s. = not significant.

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Three-Dimensional Gait Analysis

Kinematics

The patients in both groups walked more slowly initially after surgery, and a significant increase in walking speed was seen only from E1 to E3 in the medial hamstring lengthening group. Cadence initially decreased after surgery in both groups but increased in the following years. Stride length increased significantly between E1 and E3 when both groups were considered together. However, when the groups were considered separately, the increase in stride length was only significant for the medial hamstring lengthening group.

The Gillette Gait Index was reduced significantly one year after surgery. The improvements in the Gillette Gait Index were maintained at the time of the long-term follow-up, and a significant difference in the Gillette Gait Index was shown between the long-term follow-up and baseline evaluations (Table III).

An increased mean pelvic tilt was found one year after surgery for both groups, particularly in the combined medial and lateral hamstring lengthening group (Table III). Pelvic tilt significantly decreased between E1 and E2 but showed another tendency for increase at the time of the long-term follow-up.

A significant reduction in knee flexion at initial contact, minimum knee flexion in stance, and mean knee flexion in stance was present in both groups initially after surgery (Table III). Minimum knee flexion in stance was reduced significantly by 17° for the medial hamstring lengthening group and by 28° for the combined medial and lateral hamstring lengthening group with respect to reference values. Over the years, a significant deterioration was found in all three knee kinematic parameters for all patients in comparison with E1 (Table III, Fig. 2), with 9° of deterioration noted for the minimum knee flexion in stance. Most of the deterioration was noted during the first three years after surgery. While the medial hamstring lengthening group showed a significant recurrence of minimum knee flexion in stance, the deterioration in the combined medial and lateral hamstring lengthening group was not significant. Comparison of long-term outcome and baseline values for the knee kinematic parameters in all patients showed that a significant improvement still could be found for the combined medial and lateral hamstring lengthening group but not for the less-involved medial hamstring lengthening group.

Fig. 2

Histogram showing the development of minimum knee flexion in stance (given as the mean and the standard deviation) at E0 (preoperatively), E1 (one year postoperatively), E2 (two to four years [mean, three years] postoperatively), and E3 (six to twelve years [mean, eight years] postoperatively) for all patients (n = 39), for the medial hamstring lengthening (MHL) group (n = 30), and for the combined medial and lateral hamstring lengthening (CHL) group (n = 9). Positive values indicate knee flexion. *Significant difference between E0 and E1 (p < 0.001). †Significant difference between E0 and E3 (p < 0.01). #Significant difference between E1 and E2 (p < 0.05). n.s. = not significant.

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The average sagittal plane kinematics of the pelvis, hip, knee, and ankle at baseline, E1, E2, and E3 are shown in Fig. 3. The reference data for physiologic gait (twenty-four age-matched normalized patients) also are presented.

Fig. 3

Average sagittal plane kinematics as shown on gait analysis for all patients (n = 39) at E0 (preoperatively), E1 (one year postoperatively), E2 (two to four years [mean, three years] postoperatively), and E3 (six to twelve years [mean, eight years] postoperatively). The mean is represented by the blue line, the standard deviation is represented by the lucent blue area, and age-matched normalized data are represented by the gray area. Positive values indicate anterior pelvic tilt, hip flexion, knee flexion, and ankle dorsiflexion.

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Kinetics

Kinetic data could not be recorded for patients who used a walking device but were recorded for the nineteen patients who were able to walk freely at all four examination dates. The maximum internal knee flexion moment for these nineteen patients was reduced at E1. This moment was recovered between E1 and E2 and was maintained at E3. The maximum knee extensor moment increased over the years. These changes were not significant.

Adverse Effects

The number of limbs showing genu recurvatum was calculated (Table IV). Genu recurvatum was defined as knee hyperextension of >5° in stance phase. At E1, genu recurvatum was found in eighteen patients (twenty-seven limbs, 35%), with nine patients having bilateral involvement and nine patients having unilateral involvement. At E2, the number decreased significantly to ten limbs (including six limbs in patients who had had bilateral involvement at E1 and four limbs in patients who had had unilateral involvement at E1). At the time of long-term follow-up, genu recurvatum was maintained in nine limbs (12%). No significant differences were found between the medial hamstring lengthening and combined medial and lateral hamstring lengthening groups in terms of genu recurvatum at any of the postoperative examinations. At E1, genu recurvatum occurred mainly in Groups II and III (representing 56% and 26% of the cases, respectively), with only 19% of the cases occurring in Group IV (the crouch group). At the time of long-term follow-up, there were no knee hyperextensions in Group IV, whereas residual genu recurvatum was observed in nine limbs in Groups II (eight) and III (one).

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TABLE IV Adverse Effects*†

	E1	E2	E3
Genu recurvatum‡
All (n = 78)	27	10§	9§
Medial hamstring lengthening (n = 60)	21	7	7
Combined medial and lateral hamstring lengthening (n = 18)	6	3	2
Group II (jump knee) (n = 33)#	15	8	8
Group III (apparent equinus) (n = 33)#	7	2	1
Group IV (crouch) (n = 12)#	5	0	0
Increased pelvic tilt**
All (n = 78)	38	30§	36§
Medial hamstring lengthening (n = 60)	26	22	24
Combined medial and lateral hamstring lengthening (n = 18)	12	8	12

*The total number of limbs showing genu recurvatum or increased pelvic tilt is shown for all groups and examinations.
†E1 = one year postoperatively, E2 = two to four years (mean, three years) postoperatively, and E3 = six to twelve years (mean, eight years) postoperatively.
‡Genu recurvatum is defined as >5° of extension in stance phase.
§Significantly different from the previous time period (McNemar test).
#Sagittal gait pattern classification according to Rodda et al.⁹ obtained from preoperative, instrumented, three-dimensional gait analysis.
**Increased pelvic tilt is defined as an increase of mean pelvic tilt of >5° in comparison with E0.

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TABLE IV Adverse Effects*†

	E1	E2	E3
Genu recurvatum‡
All (n = 78)	27	10§	9§
Medial hamstring lengthening (n = 60)	21	7	7
Combined medial and lateral hamstring lengthening (n = 18)	6	3	2
Group II (jump knee) (n = 33)#	15	8	8
Group III (apparent equinus) (n = 33)#	7	2	1
Group IV (crouch) (n = 12)#	5	0	0
Increased pelvic tilt**
All (n = 78)	38	30§	36§
Medial hamstring lengthening (n = 60)	26	22	24
Combined medial and lateral hamstring lengthening (n = 18)	12	8	12

A clinically relevant increase in mean pelvic tilt (an increase of >5° in comparison with E0) was found in thirty-eight limbs (49%) at one year postoperatively (Table IV). The prevalence of increased pelvic tilt was 67% (twelve of eighteen) in the combined medial and lateral hamstring lengthening group, compared with 43% (twenty-six of sixty) in the isolated medial hamstring group. The overall prevalence of increased pelvic tilt decreased slightly between E1 and E2 to 38% (thirty of seventy-eight), but it increased again at the time of the long-term follow-up to 46% (thirty-six of seventy-eight).

Correlation Between Static and Dynamic Parameters

The correlation coefficient between the deterioration of the popliteal angle (between E1 and E3) and the recurrence of flexed knee gait on gait analysis (as represented by minimum knee flexion in stance) was calculated for all limbs. Only a weak correlation was found between the popliteal angle and minimum knee flexion in stance (Pearson correlation, r_p = 0.29; p = 0.09).

Discussion

Introduction | Materials and Methods | Results | Discussion | Acknowledgements

Short-Term Outcome

Various short-term outcome studies have demonstrated improvement in terms of knee extension during stance phase and the popliteal angle following hamstring lengthening^21-30. However, these short-term results have been inconsistent^22,24,26-30. Comparable initial results in terms of the findings of gait analysis and the popliteal angle were found following intramuscular hamstring lengthening in the present study, corroborating these previous findings.

Long-Term Outcome

Because of central nervous system damage and growth, subsequent changes in gait pattern and joint function are expected after multilevel surgery. Investigations demonstrating results after more than three years of follow-up are rare. Adolfsen et al. reported maintained improvement at four years after intramuscular hamstring lengthening in six patients with cerebral palsy³⁵. In a four-year follow-up study after distal hamstring lengthening in ten children with cerebral palsy, Chang et al.²² found an increase in the popliteal angle but no deterioration in kinematics. Gordon et al. reported maintained improvement in the popliteal angle and peak knee extension in stance at a mean of 2.8 years after medial hamstring tenotomy in a study of twenty-nine patients with cerebral palsy²⁷. Rodda et al. reported maintained improvement in the popliteal angle and minimum knee flexion in stance in a five-year outcome study of ten patients with cerebral palsy³⁶. The authors reported a slight but nonsignificant increase in minimum knee flexion in stance.

In the present study, outcome was evaluated an average of eight years (range, six to twelve years) postoperatively, and most patients were skeletally mature at the time of long-term follow-up because the average age at the time of surgery was ten years. The period between the ages of ten and eighteen years, in which further changes in gait may develop because of growth, is crucial for long-term outcome. In contrast to all of the intermediate-term studies discussed above, a significant deterioration of dynamic parameters, including mean knee flexion in stance, knee flexion at initial contact, and minimum knee flexion in stance, was found at long-term follow-up in the present study. Surprisingly, the improvements in the Gillette Gait Index and in the Gross Motor Function Classification System level were maintained, indicating that overall functional results after single-event multilevel surgery are preserved over the long term. However, both indices are global variables, which do not take into account detailed function of specific joints. Because the knee joint plays a central role in the gait of patients with cerebral palsy, the deterioration in knee kinematic parameters should be considered when planning the treatment of flexed knee gait. Additional lateral hamstring lengthening was needed in nine patients (eighteen limbs) to achieve adequate correction intraoperatively. Subgroup analysis showed that the medial hamstring lengthening and combined medial and lateral hamstring lengthening groups had identical sagittal knee parameters at long-term follow-up, but at the cost of increased pelvic tilt in the combined medial and lateral hamstring lengthening group.

The deterioration of the popliteal angle that was noted in the present study supports the findings of previous studies³⁷. Thompson et al. proposed that the aim of flexed knee gait correction is primarily to improve function and not simply to improve static parameters³¹. The results of the present study underline that the deterioration of the popliteal angle and the recurrence of flexed knee gait as shown on three-dimensional gait analysis do not correlate well. As previously shown for other components of gait in patients with cerebral palsy, static clinical parameters are not useful as predictors of gait function^38-40. The popliteal angle is not suitable as a method for predicting outcome or as a preoperative indication for hamstring lengthening.

Recurrence of Flexed Knee Gait

Various explanations for the recurrence of flexed knee gait should be considered as flexed knee gait represents a multiplanar problem and cannot be reduced to the knee joint only. Because of deterioration of the popliteal angle, recurrent hamstring tightness during growth represents one of the most frequently discussed possible causes. Furthermore, two different types of insufficiency may lead to recurrence over the years: proximal insufficiency (hamstrings) and distal insufficiency (lever arm dysfunction). Previous investigations have demonstrated the importance of muscle length to determine the dosage of lengthening and to avoid overcorrection^41-44. Hamstring lengthening may lead to unwanted functional effects such as increased pelvic tilt (active insufficiency of the hamstrings). This may explain the first increase in pelvic tilt, seen one year postoperatively in the present study. Increased pelvic tilt may be compensated by increased lumbar lordosis or by walking with the knees in a flexed position (compensatory flexed knee gait), which may contribute to the recurrence. Further shortening of the hamstrings raises the pelvis, which may explain the improvements in pelvic position between E1 and E2. However, flexed knee gait will increase pelvic tilt again. Decreased foot lever arm, which is caused by instability of the foot or increased external or internal tibial torsion, also may cause increased knee flexion. Instability of the foot (midfoot break) frequently is seen in pes valgus, which commonly accompanies flexed knee gait¹⁰. Despite frequent osseous foot stabilization for the correction of pes valgus deformity in 53% of the limbs in the present study, flexed knee gait recurred.

Other reasons for a shortened foot lever arm are torsional deformities of the tibia^19,20 that were not treated during multilevel surgery. To our knowledge, no clinical studies have evaluated the importance of increased external tibial torsion or midfoot break with regard to the recurrence of flexed knee gait. In the present investigation, tibial malalignment was treated with supramalleolar derotation osteotomy in only five limbs at the time of multilevel surgery.

Weakness of the quadriceps muscle is another possible factor that may cause or aggravate flexed knee gait. In the present study, distal rectus femoris transfer was performed on seventy-one limbs (91%). The rectus femoris muscle contributes about 12% of the total quadriceps muscle power and mass⁴⁵, which potentially is lost when distal rectus femoris transfer is performed. Furthermore, many patients with cerebral palsy show continuous rectus femoris activity through the stance phase⁴⁶, which may lead to further weakness of the remaining vastii after distal rectus femoris transfer. Last, weight gain and increase in body mass index also may influence flexed knee gait and lead to recurrence⁴⁷.

Genu Recurvatum

Genu recurvatum is a common adverse effect of hamstring lengthening^22-24,27,35. Adolfsen et al. identified genu recurvatum as a functionally relevant complication³⁵. In the report by Kay et al., the prevalence of genu recurvatum was higher in the group that was managed with combined medial and lateral hamstring lengthening (16%)²⁴. In the present study, genu recurvatum was found in 35% of the limbs, but there was no difference between the medial hamstring lengthening and combined medial and lateral hamstring lengthening groups. Knee hyperextension mainly occurred in patients with a preoperative jump knee gait pattern despite meticulous and successful equinus correction (Fig. 3, ankle kinematics), resulting in reduction of the excessive plantar flexion/knee extension couple. Therefore, this tendency for genu recurvatum seems to be attributed mainly to hamstring lengthening. Interestingly, the number of limbs with knee hyperextension decreased significantly, indicating that knee hyperextension may resolve during the years of follow-up. However, 12% of the limbs showed residual genu recurvatum at the time of the long-term examination, and all were in patients who had had a jump knee gait pattern preoperatively. Therefore, overcorrection represents a major complication, and a jump knee gait pattern should be taken into consideration before surgery. Another explanation for genu recurvatum at the time of long-term follow-up may be a recurrence of equinus deformity. The treatment of genu recurvatum is a challenge, and strategies are limited. In the present investigation, patients who had genu recurvatum postoperatively used an ankle-foot orthosis to prevent knee hyperextension when walking long distances.

Alternative Treatment

The proximal parts of the hamstring muscles are essential for hip extension and for stabilizing the pelvis⁴⁸. The increased pelvic tilt in the present investigation supports the results of previous studies^22,23,41,49 and may represent one factor leading to recurrence. Alternative treatment strategies include the transfer of hamstring tendons to the femur to preserve the effects on the hip and pelvis^50-52. Unfortunately, only a handful of investigations have evaluated the short-term results after hamstring transfer, and, to our knowledge, no long-term reports exist^50-52. Another approach for correcting flexed knee gait is supracondylar femoral extension osteotomy used in combination with patellar tendon shortening in different investigations^53-58. Encouraging short-term results have been reported^59,60. Thus, the combination of femoral extension osteotomy and patellar tendon shortening represents our current treatment strategy. However, this approach cannot be recommended without reservation because long-term studies are lacking.

Limitations

There was a potential for selection bias in the present study that may limit the ability to generalize these results. In some locations children with cerebral palsy may not be seen for follow-up after the age of sixteen years. This is one possible reason for the general lack of long-term reports. In the present study, sixty-eight patients were eligible for reevaluation, of whom only thirty-nine (57%) returned for long-term follow-up.

Furthermore, the reported outcome may be influenced by other procedures that were performed at the time of multilevel surgery⁶¹. Therefore, the results of the present study should be interpreted as a cumulative effect of multilevel surgery, with hamstring lengthening representing one central procedure for knee function.

For the treatment of flexed knee gait, intramuscular hamstring lengthening as a part of multilevel surgery provides satisfactory short-term improvements in knee function during gait. However, the results of the present long-term study showed a significant recurrence of flexed knee gait. Increased pelvic tilt, found in approximately 50% of the limbs postoperatively, may be one factor leading to recurrence. Genu recurvatum, a possible consequence of overcorrection with hamstring lengthening, was seen frequently at one year postoperatively. Genu recurvatum may disappear over the years, but it remains a functional problem for patients with a preoperative jump knee gait pattern. Careful selection for surgery and appropriate hamstring lengthening are needed for those patients. Knowledge about the long-term effects and possible recurrence is of greatest interest when planning treatment and should be considered when providing preoperative information to patients and their parents. Extension osteotomy of the femur in combination with patellar advancement as a current alternative treatment strategy has led to encouraging short-term results^59,60, but it remains to be seen if these short-term results are maintained at long-term follow-up.

Acknowledgements

Introduction | Materials and Methods | Results | Discussion | Acknowledgements

Note: We (the authors) cordially thank our mentor Leo Döderlein, the former leader of our cerebral palsy unit, who is now chief of staff in the Pediatric Orthopaedic Hospital in Aschau, Germany, for his inspiring support throughout all the years we worked together in Heidelberg.

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Topics

gait ; cerebral palsy ; knee joint ; gait analysis ; muscle lengthening ; pediatric surgery ; spastic diplegia ; posterior muscle of thigh ; knee flexion ; knee hyperextension deformity

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Thomas Dreher, Dóra Vegvari, Sebastian I. Wolf, Andreas Geisbüsch, Simone Gantz, Wolfram Wenz, Frank Braatz; Development of Knee Function After Hamstring Lengthening as a Part of Multilevel Surgery in Children with Spastic DiplegiaA Long-Term Outcome Study. The Journal of Bone & Joint Surgery. 2012 Jan;94(2):121-130.

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