The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 85, Issue 11

Scientific Articles | November 01, 2003

The Effect of Variation in Definition on the Diagnosis of Multidirectional Instability of the Shoulder

Edward G. McFarland, MD¹; Tae Kyun Kim, MD, P²; Hyung Bin Park, MD¹; Carlos A. Neira, MD³; Maria Isabel Gutierrez, MD, MSC⁴

¹ Division of Sports Medicine and Shoulder Surgery, Department of Orthopaedic Surgery, The Johns Hopkins University, 10753 Falls Road, Suite 215, Lutherville, MD 21093. E-mail address for E.G. McFarland: emcfarl@jhmi.edu
² Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, Seongnam, Kyungki-do, Korea
³ Orthopaedic Service, Hospital San Juan de Dios, Cali, Columbia
⁴ Department of Mental Hygiene, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, MD 21205

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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 The Johns Hopkins University, Baltimore, Maryland

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2003 Nov 01;85(11):2138-2144

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Abstract

Background: There currently is a wide variation in the definition of multidirectional instability of the shoulder in the literature. The purpose of this study was to determine if these variations influence the distribution of the diagnoses in a cohort of patients with shoulder instability.

Methods: A cohort of 168 patients who underwent shoulder surgery for instability of any type was studied. Statistical analysis was performed in two steps. First, the instability of the shoulder in each patient was classified with the use of four existing systems, and the number of patients classified as having multidirectional instability was compared among the classification systems. Second, the definition of multidirectional instability was modified so that the result of laxity testing was the criterion for making the diagnosis, and the changes in the distribution of patients with a diagnosis of multidirectional instability were analyzed.

Results: Classification with the four existing systems resulted in significant differences in the number of patients diagnosed as having multidirectional instability, with two (1.2%), seven (4.2%), thirteen (7.7%), and fourteen patients (8.3%) so diagnosed (p < 0.05). Modification of the definition of multidirectional instability so that it was based on laxity testing resulted in a wide variation in the number of patients diagnosed as having multidirectional instability; these numbers ranged from fourteen (8.3%) to 139 (82.7%) (p < 0.05).

Conclusions: This study demonstrated that variations in the criteria used for the diagnosis of multidirectional instability significantly affect the distribution of patients with that diagnosis. The use of laxity testing tends to result in an overestimation of the number of patients with this condition. This observation is important because the results of studies may vary if patients with traumatic instability are considered to have multidirectional instability on the basis of laxity testing. Investigators studying patients with multidirectional instability should carefully define the inclusion criteria that they used.

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Shoulder instability can be classified in several ways. One way is to distinguish between dislocation and subluxation^1-6. A second way is to classify the instability according to the etiology, such as traumatic, atraumatic, or repetitive microtrauma^4,7,8. A third way is to classify it by direction, such as anterior, posterior, inferior, or multidirectional^3-5,7,9,10. Instability can also be classified according to whether it is voluntary or involuntary^4,5,9,11-13. Some classifications combine several factors^3,4,6. One such system is the one popularized by Matsen et al.^4,14, which divides instability into two groups based on several factors including etiology, direction, type of treatment, and rehabilitation.

Multidirectional instability has been defined as instability in two directions^15-19 or in three directions^9,12,20. Neer and Foster⁵ first reported on a series of patients with multidirectional instability in 1980; all of the patients had uncontrollable, involuntary inferior subluxation or dislocation, associated with both anterior and posterior dislocations or subluxations of the shoulder.

In some studies, the diagnosis of multidirectional instability was based on the examiner's ability to subluxate the shoulder anteriorly or posteriorly, even if the patient did not have symptomatic instability in one or both of those directions^{8,15,16,18,21}. Several studies have suggested that it is possible to have multidirectional instability and still have a Bankart lesion, which is typically thought to be a sign of traumatic, unidirectional instability^15,18,20,21. Some authors have suggested that historical factors, such as a "dead arm," are critical when making a diagnosis of instability^8,22. Various authors have utilized the sulcus sign to define inferior instability, which is now known to be an indication of inferior laxity and not necessarily of inferior instability^17,23,24. Some authors have used a positive sulcus sign to indicate inferior instability and have considered instability in two directions, such as anterior-inferior or posterior-inferior instabilities, as distinct entities from multidirectional instability^25-27.

The accurate diagnosis of multidirectional instability is critical when determining the appropriate treatment. The treatment of any musculoskeletal condition depends on defining the specific pathological disorders and treating those disorders. The lack of a consistent definition of multidirectional instability makes it difficult to understand the pathoanatomy of the condition, select treatment, and assess outcome. While variations in definitions are a general problem in orthopaedics, they are particularly a problem in the diagnosis of multidirectional instability as knowledge of the relevant anatomy, biomechanics, clinical assessment, and treatment options continues to evolve. A capsular shift operation is thought to be the treatment of choice for multidirectional instability^{2,9,12,15,16,18,20,21}. Patients with traumatic instability who are diagnosed as having multidirectional instability may have unnecessary procedures to prevent laxity in other directions. Finally, when new procedures are described for the treatment of shoulder instability, especially multidirectional instability, it is important to know the criteria for inclusion of patients into the study in order to compare results with those in other reported series^28-32.

The purpose of this study was to determine if variations in the definition of multidirectional instability influence the distribution of the diagnoses in a cohort of patients with shoulder instability. Our hypothesis was that variations in the definition of multidirectional instability significantly change the distribution of diagnoses in a cohort of patients with shoulder instability. Specifically, it was hypothesized that definitions based on laxity testing result in the overdiagnosis of multidirectional instability.

Materials and Methods

Materials and Methods | Results | Discussion | Appendix | References

All patients from the senior author's practice (E.G.McF.) who underwent surgery for shoulder instability of any type from 1992 to 2001 were entered prospectively into this study. The patients were from a university-based practice, and the referrals were from a variety of sources: there were self-referrals, physician referrals, athletes from several sources, and Workers' Compensation cases. All patients gave informed consent prior to their procedure, and the study was approved by our institutional review board.

One hundred and sixty-eight patients underwent a total of 183 procedures for glenohumeral instability of any type. One patient had one procedure on both shoulders, six had two procedures on the same shoulder after failure of the initial procedure, one had three procedures on the same shoulder, one had four procedures on the same shoulder, and one had one procedure on one shoulder and three on the other shoulder. The average age was twenty-six years, with a range of thirteen to sixty-one years. There were 117 male patients and fifty-one female patients. The symptomatic shoulder was the dominant shoulder in 111 patients (66.1%) and the nondominant shoulder in fifty-seven.

A thorough preoperative history, with specific attention paid to etiology, previous treatment, and symptoms, was recorded for all patients. The preoperative physical examination included measurement of the active and passive ranges of motion, strength testing, and standard maneuvers to test for instability, which included an apprehension test¹, sulcus test⁵, and relocation test³³.

At the time of surgery, all patients had general anesthesia with or without a scalene block, so all had a flaccid extremity during the operation. All patients had an examination under anesthesia while in the supine position. Laxity testing was performed on both shoulders and included testing for the sulcus sign and for the anterior and posterior drawer signs as described by Gerber and Ganz³⁴. The amount of translation was described with use of a modified Hawkins scale, which categorizes humeral head translation as normal (type 0), translation to the glenoid rim (type I), translation over the glenoid rim (type II), or the humeral head locked out (type III)¹. We modified this scale to eliminate type 0 since the distinction between type 0 and type I is not clinically relevant³⁵. The sulcus sign was graded with use of an established scale, with I defined as <1.0 cm; II, as 1.0 to 2.0 cm; and III, as >2.0 cm¹⁵.

A preliminary study was performed to evaluate the intraobserver and interobserver reproducibility of laxity testing³⁶. The senior author performed the anterior and posterior drawer tests on twenty-eight shoulders in fourteen volunteers and graded the results with the scale described above. He reexamined the subjects two months later, at which time he was blinded to the results of the first examination. The agreement between the two examinations was 100% (all twenty-eight shoulders) for anterior translation and 86% (twenty-four of the twenty-eight shoulders) for posterior translation. To evaluate interobserver reliability, the senior author and one sports medicine fellow examined forty-four patients. The interobserver agreement for anterior and posterior translation was 78% and 70%, respectively. These results are similar to those in the study by Levy et al.³⁷, who reported 74% intraobserver reproducibility and 78% interobserver reproducibility.

All patients underwent arthroscopy in a lateral decubitus position with the arm in an arm-holder and use of 10 lb (4.5 kg) of traction. A posterior portal was utilized in all cases, and the joint was examined systematically. Data regarding intra-articular pathology were recorded, and all arthroscopic procedures were videotaped. Particular emphasis was paid to Bankart lesions, Hill-Sachs lesions, the drive-through sign, and labral and glenoid abnormalities. A Bankart lesion was defined as a complete detachment of the anterior-inferior aspect of the labrum from the glenoid rim. Arthroscopic findings were confirmed at the time of open surgery, which was subsequently performed in all but nine patients who underwent a thermal capsulorrhaphy.

The effect of variations in the definition of multidirectional instability on the distribution of patients with the diagnosis was determined in two ways. First, we classified the instability in each patient with use of four existing classification systems^4-6,9,26, and the number of patients classified as having multidirectional instability was compared among the classification systems. Second, the definition of multidirectional instability was modified by using the results of laxity testing as the criteria for making the diagnosis, and changes in the distribution of patients with a diagnosis of multidirectional instability were analyzed.

To facilitate this analysis, we devised a five-group classification system based on the etiology of the injury and on the intra-articular lesions observed at arthroscopy. Group I included patients who had a traumatic etiology of the instability, instability in the anterior direction only, and a Bankart or Hill-Sachs lesion, or both. All of these patients had either a complete dislocation of the shoulder or a subluxation, or both. Group II included patients who had anterior unidirectional instability with no history of trauma. These patients had a Bankart or Hill-Sachs lesion but no specific traumatic event initiating the instability. All of these patients had a dislocation of the shoulder or a subluxation, or both. Group-III patients had posterior instability. Group-IV patients had symptomatic instability in more than one direction, which was either demonstrable clinically or confirmed with arthroscopy. In our definition, patients with symptomatic instability in two directions were considered to have multidirectional instability. None of these Group-IV patients had a symptomatic inferior dislocation, and all were therefore considered to have bidirectional instability. A positive sulcus sign was not used as a diagnostic criterion for inclusion in Group IV. Most of the Group-IV patients had demonstrable, voluntary posterior shoulder instability, which had become involuntary, that coexisted with traumatic anterior instability. The anterior instability was demonstrated clinically or confirmed by the presence of a Bankart or Hill-Sachs lesion, or both. Group V included patients who had a presumed diagnosis of instability based on the history and physical examination. These patients had no history of trauma or of a subluxation or dislocation, but all had pain with activity. All had a positive relocation or apprehension maneuver for pain, but the only intraoperative finding was a positive drive-through sign^1,35,38. After the instability was classified by these criteria, the number of patients in each group was recalculated with the defining criteria for multidirectional instability based on the results of laxity testing.

Statistical analysis was performed with the SPSS software package (version 10.0; SPSS, Chicago, Illinois), and the 95% confidence interval of the proportion of patients with multidirectional instability in each classification was calculated. The significance of differences in the proportion of patients with multidirectional instability after reclassification was determined by an analyzing method for proportions in two independent groups³⁹. Significance was set at p < 0.05.

Results

Materials and Methods | Results | Discussion | Appendix | References

Classification with the four systems available in the literature resulted in large differences in the numbers of patients diagnosed as having multidirectional instability (Table I). According to the strict criteria of Neer and Foster⁵, two patients (1.2%) had multidirectional instability (instability in three directions). With the classification system of Matsen et al.⁴, seven patients (4.2%) met the criteria for multidirectional instability. Thirteen patients (7.7%) met the criteria for multidirectional instability according to the classification system of Allen²⁶, and fourteen patients (8.3%) did so according to the system of Gerber^6,18. These proportional differences among the four classification systems were significant (p < 0.05).

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TABLE I Distribution of Diagnoses Among 168 Patients According to Existing Classification Systems

Study	Group in Classification*	No. of Patients	Percent (95% Confidence Interval) with Multidirectional Instability	Significance of Difference†
Neer and Foster⁵‡	Multidirectional instability	2	1.2 (0.3-4.2)	p = 0.004, p = 0.001
Matsen et al.⁴	TUBS	80
	AMBRII	7	4.2 (2.0-8.3)
	Does not fit either type above	81
Allen²⁶	Anterior instability	108
	Posterior instability	10
	Multidirectional instability	13
	Type I (global)	8
	Type II (anterior-inferior instability with underlying hyperlaxity)	5	7.7 (4.6-12.2)	p = 0.004
	Type III (posterior-inferior instability with underlying hyperlaxity)	0
	Type IV (anterior-posterior instability)	0
	Does not fit any type above	37
Gerber^6,18	Chronic, locked dislocation	0
	Unidirectional instability without hyperlaxity	113
	Unidirectional instability with multidirectional hyperlaxity	10
	Multidirectional instability	14	8.3 (5.0-13.5)	p = 0.001
	Multidirectional instability without hyperlaxity	10
	Multidirectional instability with hyperlaxity	4
	Voluntary instability	2
	Does not fit any type above	29

TUBS = traumatic, unilateral, Bankart lesion, surgery, and AMBRII = atraumatic, multidirectional, bilateral, rehabilitation, inferior capsular shift, rotator interval. †The significance of differences in the proportion of patients diagnosed with multidirectional instability as a result of reclassification was determined by an analyzing method for proportions in two independent groups³⁹. Differences between the classification system of Neer and Foster and Allen's classification and between the classification system of Neer and Foster and Gerber's classification were significant (p = 0.004 and p = 0.001, respectively). The differences between the other classification systems were not significant (p > 0.05). ‡In the classification system proposed by Neer⁹, multidirectional instability was not defined as a separate group; only the etiologic factors were used as the defining criterion for the three-category classification system: atraumatic, traumatic, and acquired. In this table, the number of patients with a diagnosis of multidirectional instability was calculated with use of the defining criteria described in his original paper⁵.

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TABLE I Distribution of Diagnoses Among 168 Patients According to Existing Classification Systems

Study	Group in Classification*	No. of Patients	Percent (95% Confidence Interval) with Multidirectional Instability	Significance of Difference†
Neer and Foster⁵‡	Multidirectional instability	2	1.2 (0.3-4.2)	p = 0.004, p = 0.001
Matsen et al.⁴	TUBS	80
	AMBRII	7	4.2 (2.0-8.3)
	Does not fit either type above	81
Allen²⁶	Anterior instability	108
	Posterior instability	10
	Multidirectional instability	13
	Type I (global)	8
	Type II (anterior-inferior instability with underlying hyperlaxity)	5	7.7 (4.6-12.2)	p = 0.004
	Type III (posterior-inferior instability with underlying hyperlaxity)	0
	Type IV (anterior-posterior instability)	0
	Does not fit any type above	37
Gerber^6,18	Chronic, locked dislocation	0
	Unidirectional instability without hyperlaxity	113
	Unidirectional instability with multidirectional hyperlaxity	10
	Multidirectional instability	14	8.3 (5.0-13.5)	p = 0.001
	Multidirectional instability without hyperlaxity	10
	Multidirectional instability with hyperlaxity	4
	Voluntary instability	2
	Does not fit any type above	29

When the 168 patients were classified with our five-group classification system, the majority were placed in group I, and fourteen (8.3%) were classified as having multidirectional instability (Table II). A total of 111 patients (66.1%) had a history of trauma. Seventy-seven patients (45.8%) were injured in an athletic event, and twenty-one athletes (12.5% of all patients) engaged in a sports activity that involved throwing. Of all of the patients, regardless of group, ninety-one (54.2%) had a Bankart lesion, 106 (63.1%) had a Hill-Sachs lesion, and 128 (76.2%) had a positive drive-through sign.

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TABLE II Distribution of Initial Instability Classifications Among 168 Patients

Group	Description	No. (%) of Patients
I	Anterior instability with trauma	84 (50.0)
II	Anterior instability without trauma	29 (17.3)
III	Posterior instability	10 (6.0)
IV	Multidirectional instability	14 (8.3)
V	Pain only	31 (18.5)
Total		168

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TABLE II Distribution of Initial Instability Classifications Among 168 Patients

Group	Description	No. (%) of Patients
I	Anterior instability with trauma	84 (50.0)
II	Anterior instability without trauma	29 (17.3)
III	Posterior instability	10 (6.0)
IV	Multidirectional instability	14 (8.3)
V	Pain only	31 (18.5)
Total		168

Laxity testing with the patient under anesthesia revealed that a majority of the shoulders could be subluxated over the glenoid rim anteriorly or posteriorly. The findings of the laxity examinations in each group are shown in Table III. A grade-III sulcus sign was much less common (found in nine [5.4%] of the 168 patients) than a grade-I or II sulcus sign (found in seventy-three [43.5%] and eighty-six [51.2%], respectively) (p < 0.05).

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TABLE III Distribution of Results of Laxity Examinations in Each Group

	Results of Laxity Examinations*
Group (No. of Patients)	Anterior Laxity^1,34,35			Posterior Laxity^1,34,35			Inferior Laxity¹⁵
Grade I	Grade II	Grade III	Grade I	Grade II	Grade III	Grade I	Grade II	Grade III
I (84)	3 (3.6)	61 (72.6)	20 (23.8)	10 (11.9)	73 (86.9)	1 (1.2)	36 (42.9)	44 (52.4)	4 (4.8)
II (29)	2 (6.9)	26 (89.7)	1 (3.4)	6 (20.7)	23 (79.3)	0	15 (51.7)	14 (48.3)	0
III (10)	1 (10.0)	9 (90.0)	0	0	8 (80.0)	2 (20.0)	7 (70.0)	2 (20.0)	1 (10.0)
IV (14)	2 (14.3)	11 (78.6)	1 (7.1)	3 (21.4)	9 (64.3)	2 (14.3)	5 (35.7)	7 (50.0)	2 (14.3)
V (31)	3 (9.7)	28 (90.3)	0	7 (22.6)	24 (77.4)	0	10 (32.3)	19 (61.3)	2 (6.5)
Total (168)	11 (6.5)	135 (80.4)	22 (13.1)	26 (15.5)	137 (81.5)	5 (3.0)	73 (43.5)	86 (51.2)	9 (5.4)

Data are given as the number of patients, with the percentage in parentheses.

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TABLE III Distribution of Results of Laxity Examinations in Each Group

	Results of Laxity Examinations*
Group (No. of Patients)	Anterior Laxity^1,34,35			Posterior Laxity^1,34,35			Inferior Laxity¹⁵
Grade I	Grade II	Grade III	Grade I	Grade II	Grade III	Grade I	Grade II	Grade III
I (84)	3 (3.6)	61 (72.6)	20 (23.8)	10 (11.9)	73 (86.9)	1 (1.2)	36 (42.9)	44 (52.4)	4 (4.8)
II (29)	2 (6.9)	26 (89.7)	1 (3.4)	6 (20.7)	23 (79.3)	0	15 (51.7)	14 (48.3)	0
III (10)	1 (10.0)	9 (90.0)	0	0	8 (80.0)	2 (20.0)	7 (70.0)	2 (20.0)	1 (10.0)
IV (14)	2 (14.3)	11 (78.6)	1 (7.1)	3 (21.4)	9 (64.3)	2 (14.3)	5 (35.7)	7 (50.0)	2 (14.3)
V (31)	3 (9.7)	28 (90.3)	0	7 (22.6)	24 (77.4)	0	10 (32.3)	19 (61.3)	2 (6.5)
Total (168)	11 (6.5)	135 (80.4)	22 (13.1)	26 (15.5)	137 (81.5)	5 (3.0)	73 (43.5)	86 (51.2)	9 (5.4)

Data are given as the number of patients, with the percentage in parentheses.

Using various combinations of the results of laxity testing as the criterion for multidirectional instability resulted in significantly different numbers of patients being diagnosed with multidirectional instability; the numbers differed not only from those obtained with the initial classification but also among the reclassification groups (Table IV). When multidirectional instability was defined as a positive sulcus sign (grade II or III), 100 patients (59.5%) had the diagnosis of multidirectional instability. When multidirectional instability was defined as positive anterior and posterior drawer tests (Hawkins type II or III), 139 (82.7%) patients had the diagnosis.

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TABLE IV Results of Reclassification with Use of Different Criteria for Multidirectional Instability Based on Findings of Laxity Examinations

Initial Classification		Reclassification*(No. [%] of Patients)
Description	No. (%) of Patients	A	B	C	D	E
Group I: anterior instability with trauma	84 (50.0)	36 (21.4)	13 (7.7)	42 (25.0)	38 (22.6)	40 (23.8)
Group II: anterior instability without trauma	29 (17.3)	15 (8.9)	7 (4.2)	17 (10.1)	15 (8.9)	17 (10.1)
Group III: posterior instability	10 (6.0)	7 (4.2)	1 (0.6)	7 (4.2)	7 (4.2)	7 (4.2)
Group IV: multidirectional instability	14 (8.3)	100 (59.5)†	139 (82.7)†	88 (52.4)†	97 (57.7)†	90 (53.6)†
Group V: pain only	31 (18.5)	10 (6.0)	8 (4.8)	14 (8.3)	11 (6.5)	14 (8.3)

A = positive sulcus sign (grade II or III); B = positive anterior and posterior drawer signs (Hawkins¹ type II or III); C = positive anterior and posterior drawer signs and positive sulcus sign; D = positive anterior drawer sign and positive sulcus sign; and E = positive posterior drawer sign and positive sulcus sign. †The significance of differences in the proportion of patients diagnosed with multidirectional instability as a result of reclassification was determined by an analyzing method for proportions in two independent groups³⁹. All reclassifications resulted in significantly different proportions of patients being diagnosed with multidirectional instability compared with the proportions resulting from the initial classification (p < 0.001). The proportion resulting from reclassification A was significantly different from the proportions resulting from all other reclassifications (p < 0.001).

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TABLE IV Results of Reclassification with Use of Different Criteria for Multidirectional Instability Based on Findings of Laxity Examinations

Initial Classification		Reclassification*(No. [%] of Patients)
Description	No. (%) of Patients	A	B	C	D	E
Group I: anterior instability with trauma	84 (50.0)	36 (21.4)	13 (7.7)	42 (25.0)	38 (22.6)	40 (23.8)
Group II: anterior instability without trauma	29 (17.3)	15 (8.9)	7 (4.2)	17 (10.1)	15 (8.9)	17 (10.1)
Group III: posterior instability	10 (6.0)	7 (4.2)	1 (0.6)	7 (4.2)	7 (4.2)	7 (4.2)
Group IV: multidirectional instability	14 (8.3)	100 (59.5)†	139 (82.7)†	88 (52.4)†	97 (57.7)†	90 (53.6)†
Group V: pain only	31 (18.5)	10 (6.0)	8 (4.8)	14 (8.3)	11 (6.5)	14 (8.3)

Discussion

Materials and Methods | Results | Discussion | Appendix | References

This study demonstrated that variations in the definition of multidirectional instability significantly influence the number of patients who are given that diagnosis. While many previous authors have noted the problems with the definition of multidirectional instability, to our knowledge we are the first to demonstrate statistically the effect of varying the definition on the distribution of patients diagnosed with shoulder instability. This has important implications with regard to treatment, including the choice of nonoperative or operative treatment.

Our exhaustive review of the English-language literature from 1980 to 2002 revealed no consistent reporting of the criteria utilized for making the diagnosis of multidirectional instability (see Appendix). Some defined multidirectional instability as instability in two directions^26,40, and others defined it as instability in three directions^5,20. Often, when investigators used the results of laxity testing as a criterion for the diagnosis of multidirectional instability, they did not report the technique used for the laxity testing, the method of grading the laxity^20,41,42, or whether the laxity testing was done with the patient under anesthesia (Table I). Several studies included patients with a Bankart lesion, suggesting that some patients had traumatic instability as a component of the multidirectional instability^20,27,29,41. For a classification system to be helpful, it must meet several criteria. First, there should be well-defined pathological findings that are distinguishable from each other in each diagnostic category. The classification should allow evaluation of different pathological entities that may influence outcome, such as a lesion in the rotator cuff interval or a superior labral lesion. Second, the system should be reproducible and reliable between observers. Third, it should guide treatment and predict results based on that treatment. The current classifications of shoulder instability have not met these criteria completely, particularly as they relate to multidirectional instability.

There are several reasons for the myriad of definitions of multidirectional instability. First, the original criteria described by Neer were based on the sulcus sign^5,12, which is now known to be a sign of inferior laxity and not necessarily of instability^17,23,24. Although Neer reported that all of his patients had symptoms of instability with sulcus testing, many now interpret a positive sulcus sign with or without symptoms as a sign of inferior instability^20,44. As a result, patients with traumatic anterior instability who have a large sulcus sign are diagnosed as having multidirectional or bidirectional instability whether or not they have symptoms of instability with a sulcus sign.

Second, while Neer recommended that multidirectional instability be defined as instability in three directions, bidirectional instability frequently has been included as multidirectional instability in the literature^26,40,44,45. Bidirectional instability can have three different patterns (anterior-inferior, anterior-posterior, and posterior-inferior), which can be difficult to distinguish from unidirectional instability.

Third, the Neer definition of multidirectional instability includes symptomatic subluxations and dislocations^5,12, but subsequent authors rarely defined multidirectional instability as symptoms in all directions of subluxation of the shoulder on laxity testing^20,29,40,46. The ability to subluxate the shoulder with the patient either awake or under anesthesia has been interpreted by many as a sign of instability^15,40,47. There is adequate evidence in the literature to suggest that the ability to subluxate the humeral head over the glenoid rim is a normal variant and should be considered instability only if it reproduces symptoms^{6,17,18,23,24,48}. Our study demonstrated that previous studies of the results of surgical treatment of multidirectional instability need to be interpreted with close attention to how the particular authors defined multidirectional instability.

There are several limitations to our study. First, the patient population was a selected, not a random, sample, so the initial classification utilized for the statistical comparison is limited by the cohort that was studied. The study population was small and represented only the patients of one physician in an academic center. The cases in this study may not represent the entire spectrum of instability that can present for treatment, and this could have caused the statistical differences to be greater than they actually are. There were some patients who could have been placed into one group rather than into another if different criteria had been utilized for defining the initial groups. In addition, although only one author, who was experienced in the examination, performed the laxity testing and used only one classification or system of laxity measures, this does not eliminate the concern over the reliability of laxity testing.

In summary, this study demonstrates that variations in the definition of multidirectional instability significantly influence the number of patients who are given that diagnosis. As a result of this study, we recommend that investigators who study multidirectional instability in the future clearly report the criteria that they used to classify multidirectional instability. They should define whether the instability was in two or three directions. A sulcus sign should not be considered a sign of instability unless it reproduces symptoms of instability or there are intra-articular findings to suggest that it is pathological. When the results of laxity testing are used as a criterion for multidirectional instability, the authors should describe who performed the testing and whether it was done in the physician's office or with the patient under anesthesia. The degree of translation should be specified with use of recognized measures. It should be reported whether the laxity testing produced symptoms of instability. Finally, when pain with laxity testing is interpreted as a sign of instability, the authors should specify that the patient had pain, not instability, with laxity testing. Larger cohorts of patients and future study will be needed to create a useful and accurate classification system of shoulder instability that accounts for these variables.

Appendix

Materials and Methods | Results | Discussion | Appendix | References

A table summarizing the variations in the definitions of multidirectional instability in the literature is available with the electronic versions of this article, on our web site at (go to the article citation and click on "Supplementary Material") and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM).

References

Materials and Methods | Results | Discussion | Appendix | References

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Topics

shoulder region ; shoulder instability ; sulcus sign

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Edward G. McFarland, Tae Kyun Kim, Hyung Bin Park, Carlos A. Neira, Maria Isabel Gutierrez; The Effect of Variation in Definition on the Diagnosis of Multidirectional Instability of the Shoulder. The Journal of Bone & Joint Surgery. 2003 Nov;85(11):2138-2144.

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