Medial patellofemoral ligament reconstruction for patellar instability in patients with hypermobility

Transcription

1 N. R. Howells, J. D. Eldridge From Bristol Royal Infirmary, Bristol, United Kingdom KNEE Medial patellofemoral ligament reconstruction for patellar instability in patients with hypermobility A CASE CONTROL STUDY Hypermobility is an acknowledged risk factor for patellar instability. In this case control study the influence of hypermobility on clinical outcome following medial patellofemoral ligament (MPFL) reconstruction for patellar instability was studied. A total of 25 patients with hypermobility as determined by the Beighton criteria were assessed and compared with a control group of 50 patients who were matched for age, gender, indication for surgery and degree of trochlear dysplasia. The patients with hypermobility had a Beighton Score of 6; the control patients had a score of < 4. All patients underwent MPFL reconstruction performed using semitendinosus autograft and a standardised arthroscopically controlled technique. The mean age of the patients was 25 years (17 to 49) and the mean follow-up was 15 months (6 to 30). Patients with hypermobility had a significant improvement in function following surgery, with reasonable rates of satisfaction, perceived improvement, willingness to repeat and likelihood of recommendation. Functional improvements were significantly less than in control patients (p < 0.01). Joint hypermobility is not a contraindication to MPFL reconstruction although caution is recommended in managing the expectations of patients with hypermobility before consideration of surgery. N. R. Howells, MRCS, MSc, Specialist Registrar in Trauma and Orthopaedics J. D. Eldridge, FRCS(Orth), Consultant Orthopaedic Surgeon Bristol Royal Infirmary, Upper Maudlin Street, Bristol BS2 8HW, UK. Correspondence should be sent to Mr N. R. Howells; nickrhowells@yahoo.co.uk 2012 British Editorial Society of Bone and Joint Surgery doi: / x.94b $2.00 J Bone Joint Surg Br 2012;94-B: Received 13 March 2012; Accepted after revision 14 August 2012 The incidence of primary patellar dislocation has been quoted as 5.8 per in the general population, and is 29 per in adolescents. 1,2 Rates of recurrence in the literature range from 15% to 44%. 1,2 Following a single recurrent episode there is a 50% chance of further dislocation and many patients continue to have pain and mechanical symptoms. 3 Patients with generalised hypermobility have both an increased incidence of isolated dislocation of the patella and an increased risk of subsequent instability. 4-7 Patellar instability is increasingly being managed surgically with reconstruction of the medial patellofemoral ligament (MPFL). There is limited but growing evidence that these techniques can lead to excellent functional outcome Generalised hypermobility is assessed according to the criteria described by Beighton, Solomon and Soskolne. 12 Its prevalence is between 10% to 20%. 13 Hypermobility can be associated with joint symptoms, 14 and it is thought that surgical outcomes in hypermobile patients may be inferior to those in patients without hypermobility. 13 We are unaware of any published data assessing the outcome of MPFL reconstruction specifically in patients with hypermobility. This study is a prospective analysis of the influence of hypermobility on clinical outcome following MPFL reconstruction for patellar instability. Patients and Methods We performed a 2:1 frequency case-matched control study to investigate the influence of hypermobility on outcome from MPFL reconstruction for patellar instability. Data was collected prospectively on consecutive patients undergoing this procedure between October 2005 and October They were identified from a larger series of patients whose outcome has been previously reported. 11 All procedures were performed by or under the supervision of the senior author (JDE) using the standardised technique described previously. All patients were evaluated clinically and radiologically pre- and post-operatively by two authors (NRH and JDE). A total of 25 consecutive patients who met the Beighton criteria for hypermobility with a score 4 at pre-operative assessment were included in the study. The Beighton criteria for hypermobility are scored out of a maximum of nine points. Points are awarded for thumb hyperextension, wrist hyper-dorsiflexion, VOL. 94-B, No. 12, DECEMBER

2 1656 N. R. HOWELLS, J. D. ELDRIDGE Table I. Case-matching criteria Hypermobile (n = 25) Not hypermobile (n = 50) p-value Mean age (SE; range) (yrs) (1.35; 17 to 49) (1.19; 16 to 49) * Mean follow-up (SE; range) (mths) (1.33; 6 to 30) (1.21; 6 to 42) * Gender (n, %) Male 2 (8) 5 (10) Female 23 (92) 45 (90) Indication for surgery (n, %) Atraumatic dislocation 18 (72) 35 (70) Traumatic dislocation 4 (16) 7 (14) Pain and instability 3 (12) 8 (16) Grade of trochlear dysplasia (n, %) Normal 3 (12) 6 (12) Mild 14 (56) 24 (48) Moderate 8 (32) 20 (40) * t-test chi-squared test Table II. Comparison of subjective question responses between hypermobile and control patients Subjective question response of YES (n, %) Hypermobile (n = 25) Not hypermobile (n = 50) p-value (t-test) Are you satisfied with the outcome of the operation? 19 (76) 47 (94) Did the operation improve or abolish your symptoms? 19 (76) 47 (94) Would you have the same procedure again? 22 (88) 48 (96) Would you recommend this procedure to others? 21 (84) 48 (96) Have you had a recurrence of your symptoms? 8 (32) 4 (8) Have you resumed sport/activity? 9 (36) 41 (82) < Do you have any residual symptoms? 18 (72) 16 (32) elbow hyperextension and knee hyperextension on each side and achievement of hands flat on the floor with legs straight. 12 Of these 25 patients, all had a Beighton Score of 6. Eight of the 25 had a diagnosis of joint hypermobility syndrome with associated multifocal arthralgia. 13,14 These patients were matched with 50 patients who had a score of < 4 pre-operatively. Patients were matched for age, gender, indication for surgery and degree of trochlear dysplasia as described below on MRI scan (Table I). No patient was lost to follow-up. The mean age was 25.4 years (17 to 49) and 26.1 years (16 to 49) in the hypermobile and control groups, respectively. In the hypermobile group 23 patients (92%) were women and in the control group 45 (90%) were women. The mean follow-up was 16 months (6 to 42). Indications for surgery were recurrent patellar dislocation following an atraumatic or a traumatic initial dislocation, or patellar instability with pain. The most frequent indication was atraumatic recurrent dislocation, comprising 18 (72%) of the hypermobile patients and 35 (70%) of the control patients (Table I). Trochlear dysplasia was graded from MRI scans by an author (NRH) as: 1) normal; 2) mild (a shallow trochlear groove); 3) moderate (a flat surface); or 4) severe (a domed trochlea). We have previously described use of this straightforward classification. 11 It is the authors opinion that in clinical practice this is a more useful and reproducible system than the classification system of Dejour et al. 15 Severe trochlear dysplasia was an exclusion criteria for this study as the senior author (JDE) considers trochleoplasty to be more appropriate in these patients. 16 The most frequent grade of dysplasia was mild, comprising 14 (56%) of the hypermobile patients and 24 (48%) of the controls (Table I). Our surgical technique, as previously described, uses a semitendinosus autograft passed extra-synovially and attached through tunnels at the isometric points of the patella and femur with an Endobutton and interference screw respectively. 11 Patellar tracking is assessed arthroscopically through a superolateral portal before fixation of the graft to ensure correct tension and avoid medial overload. The presence of any associated chondral defects was recorded. Patients were allowed to bear full weight as tolerated postoperatively and underwent a standardised rehabilitation programme. They were reviewed post-operatively at two weeks, six weeks, three months, one year and annually thereafter. Outcome was assessed at a minimum of six months postoperatively using the International Knee Documentation Committee (IKDC) score, 17 Kujala score, 18 Oxford knee score (OKS), 19 Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), 20 the Fulkerson modification 21 of the Lysholm and Tegner activity scores 22 THE JOURNAL OF BONE AND JOINT SURGERY

3 MEDIAL PATELLOFEMORAL LIGAMENT RECONSTRUCTION FOR PATELLAR INSTABILITY IN PATIENTS WITH HYPERMOBILITY 1657 Table III. Comparison of outcome scores between patients with and without hypermobility Outcome score * Hypermobile (n = 25) Not hypermobile (n = 50) p-value Mean IKDC score (range) Pre-operative (26 to 62) (26 to 64) Post-operative (20 to 93) (18 to 100) < p-value Mean Kujala score (range) Pre-operative (37 to 61) (29 to 85) Post-operative (31 to 94) (34 to 100) < p-value < Mean OKS (range) Pre-operative (15 to 30) (17 to 35) Post-operative (11 to 47) (18 to 48) < p-value Mean WOMAC (range) Pre-operative (48 to 96) (48 to 92) Post-operative (6 to 100) (25 to 100) < p-value Mean Fulkerson Pre-operative (29 to 63) (27 to 82) Post-operative (17 to 95) (22 to 100) < p-value Mean Tegner level (range) Pre-operative 3.80 (3 to 5) 4.60 (1 to 9) Post-operative 4.13 (0 to 8) 5.44 (1 to 10) p-value Mean SF-12PCS (range) Pre-operative (23 to 45) (32 to 53) Post-operative (17 to 62) (21 to 66) p-value Mean SF-12MCS (range) Pre-operative (24 to 65) (29 to 63) Post-operative (52 to 65) (23 to 63) p-value * IKDC, International Knee Documentation Committee; OKS, Oxford knee score; WOMAC, Western Ontario and McMaster Universities osteoarthritis index; SF-12PCS/MCS, Short-Form 12 Physical/Mental Component Score comparison between the post-operative scores of each group (t-test) comparison between the pre- and post-operative score (t-test) and the Short-Form (SF) In addition patients were asked subjective evaluation questions requiring yes or no responses (Table II). Statistical analysis. This was performed using SPSS v16.0 (SPSS Inc., Chicago, Illinois). Kolmogorov-Smirnoff tests were performed to confirm the normality of data. Independent sample t-tests and one-way analysis of variance (ANOVA) were used where appropriate for data analysis. A p-value < 0.05 was considered statistically significant. Results There were no significant differences in the pre-operative scores between hypermobile patients and controls but a trend towards worse function in the hypermobile group (Table III). The hypermobile patients had significantly worse post-operative scores for all scoring systems (all p < 0.010) with the exception of the Mental Component Score of the SF-12, in which the hypermobile patients had a significantly better mean score than the control patients (58.88 (52 to 65) versus (23 to 63); p = 0.011) (Table III). For the hypermobile group, significant improvements were seen post-operatively for the Kujala score (p = 0.018), the OKS (p = 0.009), Fulkerson (p = 0.033) and SF-12MCS scores (p = 0.005), with improvements in the other scores that did not reach statistical significance (all p > 0.107). Significant improvements were seen between all of the pre-and post-operative outcome scores in the control group, except the Tegner activity level (p = 0.598) (Table III). There was no significant difference between the two groups for the subjective questions, with the exception of an VOL. 94-B, No. 12, DECEMBER 2012

4 1658 N. R. HOWELLS, J. D. ELDRIDGE increased rate of residual and recurrent symptoms (p = and p = 0.027, respectively) and lower rates of resuming sport in the hypermobile group (p < 0.001) (Table II). Despite not reaching statistical significance, the rates of satisfaction with outcome and effective improvement of symptoms were noticeably lower in the hypermobile group than the controls (both 76% versus 94%, both p = 0.066) There have been no recurrent patellar dislocations or subluxations. None of the hypermobile patients have required further surgery to date. One patient in the hypermobile group suffered a patellar fracture in a fall; this was treated conservatively and united without incident. In the hypermobile group there was a trend to worse outcomes in the eight patients diagnosed with joint hypermobility syndrome in comparison with the other hypermobile patients. This reached significance for the SF12-MCS (p = 0.045). The prevalence of lesions affecting the articular cartilage of the patellofemoral joint identified intra-operatively was comparable between hypermobile patients and controls (p = 0.516, t-test). In all 21 hypermobile patients (84%) and 40 control patients (80%) had no identifiable cartilage damage; three hypermobile and six control patients had associated osteochondral defects, and one hypermobile patient and three controls had grade II/III osteo-arthritic changes and one control patient had grade IV osteo-arthritic changes as assessed by the Outerbridge classification. 24 Discussion The MPFL is the primary static stabilising structure for the patella towards full extension. 25 It is inevitably damaged at the time of patellar dislocation and often heals poorly. 26,27 In vitro studies have confirmed the ability of MPFL reconstruction to prevent lateralisation of the patella. 28 Many reconstructive techniques have been described There is, however, no consensus on the most appropriate technique. Hypermobility has been implicated in a wide variety of musculoskeletal conditions including anterior cruciate ligament (ACL) injury, ankle ligament injury and instability of the shoulder as well as patellar instability. 29 Patients with hypermobility often have chronic generalised musculoskeletal symptoms due to joint laxity and multifocal arthralgia. 29 Hypermobile patients have been shown to have poor knee proprioception in comparison with matched controls. 30 They have also been shown to require longer to recover following injury. 31 This study adds to the existing literature on MPFL reconstruction by exploring the effect of hypermobility on outcome following surgery. Case matching provided appropriate controls for comparison. The distribution of age and gender between the groups was comparable. There was a marked difference in proportion of males and females identified with hypermobility and the control group was matched to reflect that. This is in keeping with previous studies assessing the epidemiology of hypermobility. 32 The indications for surgery between cases and controls were also comparable, with a slightly increased number of patients treated for pain and instability in the control group. We have previously shown that patients with this indication have a tendency towards slightly worse outcomes in comparison with other indications 11 and therefore this will not have increased the differences found. The degree of dysplasia was also comparable between the groups, again with the controls having a slightly increased proportion of patients with moderate dysplasia in whom it can be harder to achieve an excellent outcome. Patients with hypermobility who undergo MPFL reconstruction achieved significantly worse functional outcomes than controls. However, function was improved in hypermobile patients, albeit to a lesser extent than in controls. In addition their rates of satisfaction and levels of perceived improvement were not as poor as might have been expected given the difference in outcome scores and were not significantly different from those in controls, although there was a trend to reduced satisfaction. These findings appear to be independent of the degree of hypermobility and of associated chondral damage. The pre-operative level of function in the hypermobile patients in comparison with the controls is an important consideration as there was a trend to poorer function in hypermobile patients although this did not reach statistical significance. This suggests that the differences seen in function post-operatively between hypermobile patients and controls were in fact not all present pre-operatively and that proportionately the hypermobile patients improved, but by less than the controls. It is an interesting finding of this study that the rates of satisfaction and perceived improvement following surgery were still good in the hypermobile patients although not to the same extent as in controls. A large proportion of hypermobile patients remained satisfied with the outcome despite poorer functional scores. Expectations appear to play an important role, with hypermobile patients with marked patellar instability in some cases simply hoping for, and satisfied with, a stable patella rather than a highly functioning symptom free joint. Joint hypermobility is not a contraindication to MPFL reconstruction although caution is recommended in managing the expectations of patients with hypermobility before consideration of surgery. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. References 1. Fithian DC, Paxton EW, Stone ML, et al. 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