The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 86, Issue 5

Scientific Articles | May 01, 2004

Knee Stability Following Anterior Cruciate Ligament Rupture and Surgery: The Contribution of Irreducible Tibial Subluxation

Louis C. Almekinders, MD¹; Rajeev Pandarinath, BS¹; Frank T. Rahusen, MD¹

¹ North Carolina Orthopaedic Clinic, Division of Orthopaedic Surgery, Duke University Health System, 4309 Medical Park Drive, Durham, NC 27704. E-mail address for L.C. Almekinders: almek002@mc.duke.edu

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The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Investigation performed at North Carolina Orthopaedic Clinic, Division of Orthopaedic Surgery, Duke University Health System, Durham, North Carolina

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2004 May 01;86(5):983-987

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Abstract

Background: Knee stability after anterior cruciate ligament reconstruction is generally determined by measuring total anteroposterior tibial motion. In spite of a decrease in excessive anteroposterior tibial motion after anterior cruciate ligament reconstruction, problems can still develop. In the present study, we sought to define the tibiofemoral relationship more accurately with use of stress radiographs of human knees after anterior cruciate ligament rupture and after anterior cruciate ligament reconstruction.

Methods: A previously described radiographic technique was used to evaluate the position of the tibia relative to the femur with the application of an anteriorly directed tibial force and subsequently with the application of a posteriorly directed tibial force. Tibial position and total tibial translation were calculated from these radiographs. In addition, KT-1000 measurements were obtained. Three groups of patients were studied: Group 1 included twenty-eight patients with an untreated anterior cruciate ligament rupture, Group 2 included nineteen patients who had undergone a clinically successful anterior cruciate ligament reconstruction, and Group 3 included twenty-five control subjects with normal knees.

Results: KT-1000 testing showed that the average side-to-side differences in Group 1 (5.8 mm) and Group 2 (2.7 mm) were significantly different from that in Group 3 (0.8 mm) (p < 0.01 and p < 0.05, respectively). Stress radiographs showed that the average total tibial translation in Group 1 (9.8 mm) was significantly different from those in Group 2 (5.6 mm) and Group 3 (4.3 mm) (p < 0.05 and p < 0.001, respectively). Within Group 1, knees with radiographic signs of osteoarthritis were more stable, with an average total tibial excursion of 6.8 mm. The improved stability of the reconstructed knees in Group 2 and the osteoarthritic knees in Group 1 was not entirely the result of decreased anterior tibial translation; it was, in part, due to an irreducible anterior subluxation of the tibia. A posteriorly directed stress in these knees did not reduce the tibia to the anatomic position relative to the femur; the osteoarthritic knees in Group 1 were 9.9 mm short of full reduction and the knees in Group 2 were 3.1 mm short of full reduction (p < 0.01)

Conclusions: Irreducible tibial subluxation can be present in the knee following surgical reconstruction of the anterior cruciate ligament. Osteoarthritic changes following an untreated anterior cruciate ligament rupture are also associated with uncorrectable tibial subluxation along with a decrease in instability. The irreducible tibial subluxation could explain why osteoarthritic changes still may develop in stable, reconstructed knees in spite of the improved stability. Currently used arthrometric measurements, such as KT-1000 scores, do not measure this phenomenon.

Level of Evidence: Therapeutic study, Level III-2 (retrospective cohort study). See Instructions to Authors for a complete description of levels of evidence.

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Rupture of the anterior cruciate ligament is a common injury that is associated with permanent sequelae affecting knee stability and function. Symptoms of instability resulting from increased anteroposterior motion of the tibia relative to the femur often limit the activities of a patient who has an untreated anterior cruciate ligament rupture. In addition, long-term degenerative changes are frequent in knees with an untreated anterior cruciate ligament rupture^1,2. Surgical reconstruction of the ruptured anterior cruciate ligament has become a widely accepted method for minimizing the symptoms of instability. Many cohort studies have shown that excessive anteroposterior tibial motion is improved after surgical reconstruction of the anterior cruciate ligament^3,4. The improvements in stability usually are documented through physical examination tests or arthrometric examinations. In spite of these improvements, long-term degenerative changes of the knee still may occur^5,6. One study suggested that there is actually an increase in degenerative changes following surgical reconstruction of the anterior cruciate ligament⁷.

An earlier study demonstrated that improved tibial stability following reconstruction of the anterior cruciate ligament did not always result in a normal tibiofemoral relationship⁸. The abnormal tibiofemoral relationship was found to be an irreducible fixed anterior subluxation of the tibia relative to the femur. Because that initial pilot study did not include any knees with an anterior cruciate ligament injury that did not undergo reconstructive surgery, it was impossible to determine whether this abnormal tibiofemoral relationship was directly associated with the reconstructive surgery itself or was merely part of the natural history of an anterior cruciate ligament injury. Therefore, the study was expanded from twenty-nine to sixty-two subjects, and knees with anterior cruciate ligament rupture but without surgical reconstruction were also included. The present study provides information on not only the tibial stability but also the tibiofemoral relationship in normal knees, knees with a deficient anterior cruciate ligament, and knees with a reconstructed anterior cruciate ligament. On the basis of the results of reported clinical series^5,6 as well as our earlier studies, we hypothesized that surgical reconstruction of the anterior cruciate ligament improves anteroposterior tibial stability but is associated with an abnormal tibiofemoral relationship that is not found in knees with an untreated anterior cruciate ligament rupture.

Materials and Methods

Materials and Methods | Results | Discussion | References

Three groups of subjects were studied. Group 1 consisted of twenty-eight patients with a documented anterior cruciate ligament tear who had not undergone surgical reconstruction. These patients were recruited at random from our clinical database. They were not being actively followed or treated at the time of the present study, and they were not specifically age-matched with the patients in the other groups. The prerequisite for inclusion in this group was an anterior cruciate ligament tear that had occurred at least twenty-four months before the study and that had been documented on the basis of abnormal physical findings and confirmed on the basis of either magnetic resonance imaging or arthroscopy. In most cases, the arthroscopy had been performed to treat a chronic meniscal or other cartilaginous abnormality. No treatment had been performed on either cruciate ligament in any patient. All patients had a full range of motion of the knee. Group 2 consisted of nineteen patients who had sustained an anterior cruciate ligament rupture and had subsequently undergone surgical reconstruction of the ligament. Again, the patients were randomly chosen from our database. The prerequisite for inclusion in this group was a well-functioning primary reconstruction of the anterior cruciate ligament that had been performed with use of a bone-patellar ligament-bone autograft by the senior author (L.C.A.) at least twenty-four months prior to the study. Group 3 consisted of twenty-five age-matched volunteers with normal knees. Most of these subjects were patients who had been seen in our clinic for problems that were not related to the knee. The prerequisites for inclusion in this group included normal physical and arthrometric findings in both knees and no history of knee injuries.

Informed consent was obtained from all subjects on the basis of a research protocol that had been approved by the institutional review board at our institution. All subjects completed a Lysholm knee questionnaire⁹ regarding the affected knee in order to obtain a subjective assessment of the level of function. In the control group, one knee in each subject was randomly chosen for stress-testing. In all groups, both knees were then assessed with a standard physical examination that included range-of-motion testing and Lachman stress-testing. In addition, an arthrometric examination was performed with use of a KT-1000 arthrometer (MEDmetric, San Diego, California). The tibial motion resulting from a manual maximum force was used in the data analysis. Finally, stress radiographs were made with use of a Telos stress device (Telos GmbH, Marburg/Labo, Germany) as described previously^9,10. The stress radiography was done with the knees in maximum extension. First, a lateral radiograph was made with an anteriorly directed force of 66.7 N applied to the proximal part of the tibia, with the magnitude of the force determined by the load cell in the stress device. Then, a lateral radiograph was made with a posteriorly directed force of 66.7 N applied to the proximal part of the tibia. The position of the tibia relative to the femur was then measured on each radiograph as described by Franklin et al.¹⁰. First, a line was drawn along the subchondral bone plate of the tibial plateau. Next, two lines were drawn perpendicular to the first line, with one line starting at the posterior margin of the lateral tibial plateau and the other line starting at the posterior margin of the medial tibial plateau. Subsequently, the lateral and medial femoral condyles were identified on the basis of the condylopatellar sulcus laterally and the lower trochlear ridge medially. Finally, the shortest distance between each of these two lines and the most posterior extent of the lateral and medial femoral condyle, respectively, was measured. Lines that fell anterior to the posterior margin of the femoral condyle were assigned a positive value, whereas lines that fell posterior to the femoral condyle were assigned a negative value. The two values for each lateral radiograph were averaged, and the average value was used in the data analysis. Total tibial translation was calculated on the basis of a comparison of the measurements on the two lateral radiographs. In the present study, the measurements were not corrected for magnification because all radiographs were made in a standard manner. In addition to the measurements on the lateral radiographs, weight-bearing anteroposterior radiographs were scored by an independent observer (R.P.) for the presence of osteophytes and joint-space narrowing. If both findings were present, the knee was classified as having degenerative joint disease. There was not a sufficient number of knees with degenerative changes to allow further stratification on the basis of the degree of degenerative changes. It should be noted that these patients were chosen from the database because of the diagnosis of an anterior cruciate ligament rupture and not because of the diagnosis of osteoarthritis. The degenerative changes in these patients were generally mild to moderate. No knees with end-stage arthritis, flexion contractures, and/or bone-on-bone contact were seen in this study.

The differences between the groups were evaluated with an analysis of variance. Tukey post hoc analysis was used to determine the significance of the differences. The level of significance was set at p < 0.05.

Results

Materials and Methods | Results | Discussion | References

The average age was 28.6 years (range, twenty-one to thirty-eight years) for the subjects who had an untreated anterior cruciate ligament rupture, 26.3 years (range, nineteen to thirty-nine years) for the subjects who had had an anterior cruciate ligament reconstruction, and 30.1 years (range, twenty to forty-one years) for the subjects in the control group. These differences were not significant. The average interval between the time of the injury and the time of the study in the group with an untreated anterior cruciate ligament rupture was 37.8 months (range, twenty-four to seventy-four months). In this group, nine patients had undergone partial meniscectomy (six medially and three laterally) following the initial anterior cruciate ligament rupture. The average intervals between the time of the injury and the time of surgery and between the time of surgery and the time of the study in the group with a reconstructed anterior cruciate ligament were 6.1 months (range, one to fourteen months) and 34.3 months (range, twenty-four to fifty-two months), respectively. In this group, five patients had undergone partial meniscectomy (three laterally and two medially) either prior to or at the time of reconstruction. The average Lysholm score for the patients with an untreated anterior cruciate ligament rupture (Group 1) was significantly worse (p < 0.001) than the average scores for the other two groups (Table I). There was no significant difference between the patients who had had reconstruction of the anterior cruciate ligament (Group 2) and the normal control subjects (power, 0.99).

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TABLE I Lysholm Scores and KT-1000 Side-to-Side Differences for the Three Groups*

	Lysholm Score (points)	KT-1000 Side-to-Side Difference (mm)
Group 1 (anterior cruciate ligament rupture)	77 ± 19†	5.8 ± 2.3†
Group 2 (anterior cruciate ligament reconstruction)	90 ± 12	2.7 ± 2.2†
Group 3 (normal)	99 ± 3	0.8 ± 1.0

The data are given as the average and the standard deviation. †The difference was significant (p < 0.05) compared with Group 3.

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TABLE I Lysholm Scores and KT-1000 Side-to-Side Differences for the Three Groups*

	Lysholm Score (points)	KT-1000 Side-to-Side Difference (mm)
Group 1 (anterior cruciate ligament rupture)	77 ± 19†	5.8 ± 2.3†
Group 2 (anterior cruciate ligament reconstruction)	90 ± 12	2.7 ± 2.2†
Group 3 (normal)	99 ± 3	0.8 ± 1.0

The data are given as the average and the standard deviation. †The difference was significant (p < 0.05) compared with Group 3.

KT-1000 testing showed that the average side-to-side difference in Group 1 was 5.8 mm, indicating that the knees with an untreated anterior cruciate rupture had a significant increase (p < 0.01) in total anteroposterior tibial motion in comparison with the contralateral, normal knees in the same group as well as in comparison with the knees in the control group (Table I). As expected, the knees that had had surgical reconstruction of the anterior cruciate ligament (Group 2) had significantly less anteroposterior tibial motion than did the knees that had an untreated rupture of the anterior cruciate ligament (Group 1) (p < 0.05). The average side-to-side difference in Group 2 was 2.7 mm and, although this was a small increase compared with the normal knees in the control group, the difference between these two groups was still significant (p < 0.05).

All patients had a full range of knee motion without flexion contractures. When the results of stress radiography were analyzed, the total anteroposterior tibial translation that was calculated from the two stress radiographs showed a pattern that was similar to that shown by the KT-1000 data. As stress radiography was performed on only one knee in each patient, side-to-side differences could not be calculated as is commonly done with KT-1000 data. Once again, the average total tibial translation in the knees with an untreated rupture of the anterior cruciate ligament (9.8 mm) was significantly larger than that in the normal knees in the control group (p < 0.001) (Table II). Similar to the KT-1000 data, the total tibial translation in the reconstructed knees was significantly less than that in the unreconstructed knees (p < 0.05) and was not significantly different from that in the normal knees (power, 0.90).

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TABLE II Results of Stress Radiography*

	Total Tibial Translation (mm)	Maximum Anterior Position† (mm)	Maximum Posterior Position† (mm)
Group 1 (anterior cruciate ligament rupture)
All (n = 28)	9.8 ± 4.2†	+9.0 ± 4.5†	-0.8 ± 4.0†
No osteoarthritis (n = 19)	10.3 ± 4.3†	+8.0 ± 4.3†	-2.3 ± 2.2
Osteoarthritis (n = 9)	6.8 ± 2.1†	+12.8 ± 2.8†	+6.0 ± 3.2†
Group 2 (anterior cruciate ligament reconstruction)	5.6 ± 3.3	+4.8 ± 3.8†	-0.8 ± 3.1†
Group 3 (normal)	4.3 ± 2.8	+0.4 ± 2.3	-3.9 ± 2.9

The data are given as the average and the standard deviation. †Positive values indicate a more anterior tibial position, and negative values indicate a more posterior tibial position. See reference 8 for a more detailed description of the radiographic measurements. †The difference was significant (p < 0.05) compared with Group 3.

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TABLE II Results of Stress Radiography*

	Total Tibial Translation (mm)	Maximum Anterior Position† (mm)	Maximum Posterior Position† (mm)
Group 1 (anterior cruciate ligament rupture)
All (n = 28)	9.8 ± 4.2†	+9.0 ± 4.5†	-0.8 ± 4.0†
No osteoarthritis (n = 19)	10.3 ± 4.3†	+8.0 ± 4.3†	-2.3 ± 2.2
Osteoarthritis (n = 9)	6.8 ± 2.1†	+12.8 ± 2.8†	+6.0 ± 3.2†
Group 2 (anterior cruciate ligament reconstruction)	5.6 ± 3.3	+4.8 ± 3.8†	-0.8 ± 3.1†
Group 3 (normal)	4.3 ± 2.8	+0.4 ± 2.3	-3.9 ± 2.9

When the position of the tibia relative to the femur was evaluated on stress radiographs, the results showed that an improvement in total tibial translation does not necessarily mean a similar improvement in the tibiofemoral relationship. The average maximum anterior position of the tibia in knees that had had reconstruction of the anterior cruciate ligament was still significantly different from that in normal knees (+4.8 mm compared with +0.4 mm; p < 0.05). At the same time, the average maximum posterior position of the femur in knees that had had reconstruction of the anterior cruciate ligament was significantly less than that in normal knees (—0.8 mm compared with —3.9 mm; p < 0.05). Thus, the improvement in total anteroposterior tibial translation that is noted following reconstruction of the anterior cruciate ligament is accomplished not only by decreasing the maximum anterior translation but also by restricting some of the maximum posterior translation by an average of 3.1 mm (Fig. 1).

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Fig. 1: Stress radiographs made with posteriorly directed stress in a normal knee (left) and a reconstructed knee (right). Note the inability to fully reduce the tibia to its posterior position in the reconstructed knee.

When the results for all knees with an untreated anterior cruciate ligament rupture were averaged, the maximum anterior tibial position was the most abnormal of all groups. The maximum posterior tibial position of all untreated knees was similar to that of the knees that had had reconstruction of the anterior cruciate ligament. However, when the knees with an untreated anterior cruciate ligament rupture were separated into those with and without radiographic signs of osteoarthritis, a different result was found. Knees with an untreated anterior cruciate ligament rupture but without osteoarthritis had a maximum posterior tibial position that was similar to that of normal knees (—2.3 mm compared with —3.9 mm). In contrast, knees with an untreated anterior cruciate ligament rupture that had radiographic signs of osteoarthritis had a marked restriction of the maximal posterior tibial position (+6.0 mm compared with —3.9), which resulted in an average difference of 9.9 mm.

Discussion

Materials and Methods | Results | Discussion | References

Similar to the findings of the earlier study⁸, the restriction of the maximum posterior position of the tibia was found in knees that had had reconstruction of the anterior cruciate ligament. This finding indicates the presence of an anterior subluxation that cannot be fully reduced with a posteriorly directed force on the tibia. The improvement in KT-1000 scores and other measurements of total tibial translation therefore is not accomplished solely by a restriction of anterior tibial translation but appears to be partly due to a restriction of posterior translation. Therefore, total tibial translation alone cannot be used to determine whether reconstruction of the anterior cruciate ligament has restored the normal tibiofemoral relationship. The cause of the restricted posterior position of the tibia is not certain. However, in the subgroup of knees with an untreated anterior cruciate ligament rupture and no radiographic evidence of osteoarthritis, this phenomenon was not seen, despite the fact that these knees were evaluated at least two years after the injury. As the irreducible subluxation was seen in knees that had had surgical reconstruction, it is possible that surgical intervention plays a role in the early development of fixed subluxation. Intra-articular graft substitution generally requires débridement of the tissues in the intercondylar notch. Although the posterior cruciate ligament is left intact, its synovial sheath is often violated. This may cause a scarring response and a subsequent contracture of the posterior cruciate ligament, which could explain the fixed subluxation found in this study. A similar phenomenon, characterized by morphological changes in the anterior cruciate ligament¹¹ and an irreducible posterior subluxation¹², has been reported in knees with an intact anterior cruciate ligament and a chronically deficient posterior cruciate ligament. We are aware of no reports that have documented the exact role of surgery in this phenomenon, and longitudinal studies are needed to prove this concept. It is also unclear whether meniscectomy plays an important role in the observed tibial subluxation. It is possible that loss of menisci following anterior cruciate ligament rupture allows subluxation to progress. On the other hand, several of the knees without prior meniscectomy in the present study also demonstrated irreducible tibial subluxation. A statistical analysis of the role of meniscectomy was not feasible as the numbers were low and the amount of meniscal resection was variable.

One of the new findings of the current study was the presence of the irreducible subluxation in knees with an untreated anterior cruciate ligament rupture and osteoarthritic changes. Irreducible tibial subluxation was not found in knees with an untreated anterior cruciate ligament rupture but without osteoarthritic changes. Although this association with osteoarthritis does not necessarily indicate a cause-and-effect relationship, it could be one explanation. Irreducible anterior subluxation of the tibia may eventually develop in anterior cruciate ligament-deficient knees, even in the absence of reconstructive surgery. This subluxation could be the common pathway to osteoarthritis in both treated and untreated knees. The irreducible subluxation is likely to affect the normal kinematics of the knee by disturbing the normal rolling motion of the tibiofemoral joint, which may lead not only to improved stability but also to increased degenerative changes. This would also explain the findings of Daniel et al., who reported increased degenerative changes in spite of improved total anteroposterior tibial motion in knees that had had reconstruction of the anterior cruciate ligament⁷. Of course, we cannot prove this concept and it is still possible that the irreducible subluxation and degenerative changes are not causally related in this manner.

We believe that these data partially support our hypothesis that irreducible anterior tibial subluxation can occur after reconstruction of the anterior cruciate ligament. However, this finding is not unique to reconstructed knees. Irreducible subluxation also was seen in anterior cruciate ligament-deficient knees that had osteoarthritic changes. Whether the subluxation in reconstructed knees was directly related to the effects of the surgery remains uncertain but possible. In order to confirm a causal relationship between subluxation and osteoarthritis, longitudinal studies are needed in which patients are followed from the time of anterior cruciate ligament injury until after surgery or until after the development of osteoarthritis. The present study also did not involve measurements at different flexion angles or during active motion. Such studies will be needed to fully understand the changes in the tibiofemoral relationship following anterior cruciate ligament injury and surgery.

References

Materials and Methods | Results | Discussion | References

Maletius W, Messner K. Eighteen- to twenty-four-year follow-up after complete rupture of the anterior cruciate ligament. Am J Sports Med.1999; 27: 711-7.27711 1999 [PubMed]

Neyret P, Donell ST, DeJour D, DeJour H. Partial meniscectomy and anterior cruciate ligament rupture in soccer players. A study with a minimum 20-year followup. Am J Sports Med.1993;21: 455-60.21455 1993 [CrossRef]

Anderson AF, Snyder RB, Lipscomb AB Jr. Anterior cruciate ligament reconstruction. A prospective randomized study of three surgical methods. Am J Sports Med.2001;29: 272-9.29272 2001 [PubMed]

Shelbourne KD, Gray T. Anterior cruciate ligament reconstruction with autogenous patellar tendon graft followed by accelerated rehabilitation. A two- to nine-year followup. Am J Sports Med.1997;25: 786-95.25786 1997 [PubMed][CrossRef]

Jomha NM, Borton DC, Clingeleffer AJ, Pinczewski LA. Long-term osteoarthritic changes in anterior cruciate ligament reconstructed knees. Clin Orthop.1999;358: 188-93.358188 1999 [PubMed]

Lohmander LS, Roos H. Knee ligament injury, surgery and osteoarthrosis. Truth or consequences? Acta Orthop Scand.1994;65: 605-9.65605 1994 [PubMed][CrossRef]

Daniel DM, Stone ML, Dobson BE, Fithian DC, Rossman DJ, Kaufman KR. Fate of the ACL-injured patient. A prospective outcome study. Am J Sports Med.1994;22: 632-44.22632 1994 [PubMed][CrossRef]

Almekinders LC, de Castro D. Fixed tibial subluxation after successful anterior cruciate ligament reconstruction. Am J Sports Med. 2001;29: 280-3.29280 2001 [PubMed]

Lysholm J, Gillquist J. Evaluation of knee ligament surgery results with special emphasis on use of a scoring scale. Am J Sports Med.1982;10: 150-5.10150 1982 [PubMed][CrossRef]

Franklin JL, Rosenberg TD, Paulos LE, France EP. Radiographic assessment of instability of the knee due to rupture of the anterior cruciate ligament. A quadriceps-contraction technique. J Bone Joint Surg Am.1991;73: 365-72.73365 1991 [PubMed]

Ochi M, Murao T, Sumen Y, Kobayashi K, Adachi N. Isolated posterior cruciate ligament insufficiency induces morphological changes of the anterior cruciate ligament collagen fibrils. Arthroscopy.1999;15: 292-6.15292 1999 [PubMed][CrossRef]

Strobel MJ, Weiler A, Schulz MS, Russe K, Eichhorn HJ. Fixed posterior subluxation in posterior cruciate ligament-deficient knees: diagnosis and treatment of a new clinical sign. Am J Sports Med.2002;30: 32-8.3032 2002 [PubMed]

Topics

anterior cruciate ligament rupture ; knee joint ; osteoarthritis ; reconstructive surgical procedures ; tibia ; anterior cruciate ligament reconstruction

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Louis C. Almekinders, Rajeev Pandarinath, Frank T. Rahusen; Knee Stability Following Anterior Cruciate Ligament Rupture and SurgeryThe Contribution of Irreducible Tibial Subluxation. The Journal of Bone & Joint Surgery. 2004 May;86(5):983-987.

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