The management of recurrent patellar dislocation

Development of patellofemoral osteoarthritis with knee joint malalignment and lateral patellar dislocation after hindlimb suspension in growing rats

Knee malalignment is a risk factor for patellar instability and patellofemoral osteoarthritis (PFOA), but etiologies remain unknown. We investigated the potential effects of decreased weight loading during growth on knee alignments and patellofemoral (PF) joint pathology. Hindlimb suspension (HS) was performed in 4-week-old female rats for 2, 4, and 8 weeks (HS groups). Age-matched rats were used as controls. Three-dimensional reconstructed images of the knee were obtained using X-ray computed tomography. Tibial tubercle-trochlear groove (TT-TG) distance, patellar tilt angle, and bisect offset were measured as indices of knee alignment. Histological analysis was also performed to evaluate the changes in cartilage and synovium in the PF joints. At Week 8, TT-TG distance, patella tilt angle, and bisect offset were significantly larger in the HS group than in the control group, respectively, indicating tibial external rotation, outward patellar tilt, and external displacement of the patella. Lateral patellar dislocation was frequently found in the HS group at Week 8 (five of eight knee joints, p < 0.05). Degenerative changes in the cartilage of the trochlear groove were observed at Week 8, and synovial changes such as hypertrophy and synovitis were observed at Weeks 4 and 8. Correlation analyses revealed significant relationships between the Mankin score and bisect offset, and between the OARSI synovitis score and all knee alignments indices. These results suggest that decreased weight loading on the lower extremities in growing rats resulted in knee malalignments characterized by external rotation of tibia and high incidence of lateral patellar dislocation with concomitant PFOA.

Femoral Anteversion Measured by the Surgical Transepicondylar Axis Is Correlated with the Tibial Tubercle-Roman Arch Distance in Patients with Lateral Patellar Dislocation

Background and Objectives: Various predisposing factors for lateral patellar dislocation (LPD) have been identified, but the relation between femoral rotational deformity and the tibial tubercle-Roman arch (TT-RA) distance remains elusive. Materials and Methods: We conducted this study including 72 consecutive patients with unilateral LPD. Femoral anteversion was measured by the surgical transepicondylar axis (S-tAV), and the posterior condylar reference line (P-tAV), TT-RA distance, trochlear dysplasia, knee joint rotation, patellar height, and hip-knee-ankle angle were measured by CT images or by radiographs. The correlations among these parameters were analyzed, and the parameters were compared between patients with and without a pathological TT-RA distance. Binary regression analysis was performed, and receiver operating characteristic curves were obtained. Results: The TT-RA distance was correlated with S-tAV (r = 0.360, p = 0.002), but the correlation between P-tAV and the TT-RA distance was not significant. S-tAV had an AUC of 0.711 for predicting a pathological TT-RA, with a value of >18.6° indicating 54.8% sensitivity and 82.9% specificity. S-tAV revealed an OR of 1.13 (95% CI [1.04, 1.22], p = 0.003) with regard to the pathological TT-RA distance by an adjusted regression model. Conclusions: S-tAV was significantly correlated with the TT-RA distance, with a correlation coefficient of 0.360, and was identified as an independent risk factor for a pathological TT-RA distance. However, the TT-RA distance was found to be independent of P-tAV.

Anatomical Components Associated With Increased Tibial Tuberosity-Trochlear Groove Distance

Background:

Increased tibial tuberosity–trochlear groove (TT-TG) distance is an important indicator of medial tibial tubercle transfer in the surgical management of lateral patellar dislocation (LPD). Changes to TT-TG distance are determined by a combination of several anatomical factors.

Purpose:

To (1) determine the anatomical components related to increased TT-TG distance and (2) quantify the contribution of each to identify the most prominent component.

Study Design:

Case-control study; Level of evidence, 3.

Methods:

Included were 80 patients with recurrent LPD and 80 age- and body mass index–matched controls. The 2 groups were compared in TT-TG distance and its related anatomical components: tibial tubercle lateralization (TTL), trochlear groove medialization, femoral anteversion, tibiofemoral rotation (TFR), tibial torsion, and mechanical axis deviation (MAD). The Pearson correlation coefficient (r) was calculated to evaluate the association between increased TT-TG distance and its anatomical parameters, and factors that met the inclusion criteria of P < .05 and r ≥ 0.30 were analyzed via stepwise multivariable linear regression analysis to predict TT-TG distance.

Results:

The LPD and control groups differed significantly in TT-TG distance, TTL, TFR, and MAD (P < .001 for all). Increased TT-TG distance was significantly positively correlated with TTL (r = 0.376; P < .001), femoral anteversion (r = 0.166; P = .036), TFR (r = 0.574; P < .001), and MAD (r = 0.415; P < .001), and it was signficantly negatively correlated with trochlear groove medialization (r = −0.178; P = .024). The stepwise multivariable analysis revealed that higher TTL, excessive knee external rotation, and excessive knee valgus were statistically significant predictors of greater TT-TG distance (P < .001 for all). The standardized estimates that were used for evaluating the predictive values were larger for TFR compared with those for TTL and MAD.

Conclusion:

TTL, TFR, and MAD were the main independent anatomical components associated with increased TT-TG distance, with the most prominent component being TFR. The association of TT-TG distance to each component analyzed in our study may help guide surgical planning.

Combined MPFL reconstruction and tibial tubercle osteotomy for patellar instability: A retrospective review of 23 patients

The primary objective of this retrospective study is to compare patient outcomes following a combined approach (MPFL reconstruction and TTT) to outcomes reported in the literature by patients who required either only an isolated TTT procedure to treat pathologic lateral patellar instability or isolated MPFL reconstruction to treat patellar dislocation due to MPFL insufficiency. Twenty-three patients (74%) were available for follow-up and are included in our analysis. MPFL reconstruction combined with TTT has a high rate of success for patients presenting with patellar instability and extensor mechanism mal-alignment. The risk of recurrence with this technique was low (4.3%).

Coronal and Transverse Malalignment in Pediatric Patellofemoral Instability

Patellofemoral instability (PFI) encompasses symptomatic patellar instability, patella subluxations, and frank dislocations. Previous studies have estimated the incidence of acute patellar dislocation at 43 per 100,000 children younger than age 16 years. The medial patellofemoral ligament (MPFL) complex is a static soft tissue constraint that stabilizes the patellofemoral joint serving as a checkrein to prevent lateral displacement. The causes of PFI are multifactorial and not attributed solely to anatomic features within the knee joint proper. Specific anatomic features to consider include patella alta, increased tibial tubercle–trochlear groove distance, genu valgum, external tibial torsion, femoral anteversion, and ligamentous laxity. The purpose of this paper is to provide a review of the evaluation of PFI in the pediatric and adolescent patient with a specific focus on the contributions of coronal and transverse plane deformities. Moreover, a framework will be provided for the incorporation of bony procedures to address these issues.

Single-tunnel and double-tunnel medial patellofemoral ligament reconstructions have similar clinical, radiological and functional results

PURPOSE

The aim of the present study was to evaluate the clinical, radiological and functional results of patients underwent single-tunnel (ST) and double-tunnel (DT) medial patellofemoral ligament(MPFL) reconstructions with hamstring autograft following recurrent patella dislocation prospectively in a single institution.

METHODS

From 2013 to 2017, 80 patients with symptomatic recurrent patellar dislocation or instability were randomly divided into 2 groups for MPFL reconstruction with ST technique or DT technique and evaluated prospectively. In the ST group, there were 20 male and 20 female with a median follow-up of 46.5 months (range 24-74). The median age was 15 years (range 10-28). In the DT group, there were 18 male and 22 female with a median follow-up of 40 months (range 24-74). The median age was 19 years (range 14-29). Clinical scores (Kujala score, Lysholm score, Tegner score and IKDC score) and radiological measurements (congruence angle and patellar tilt angle) of the patients were evaluated preoperatively and at postoperative 24th month. Isokinetic dynamometric tests were performed at postoperative 24th month and the difference between the operated leg and the non-operated leg was found as a percentage deficit.

RESULTS

There were no postoperative complications, redislocation or subluxation in any patient. Kujala, Lysholm, Tegner and IKDC scores were better and statistically significant postoperatively in both groups (p < 0.05). However, there was no statistically significant difference between the groups (n.s.). The congruence angle and patellar tilt angle were found to be returned to normal values postoperatively, but there was no statistically significant difference between the groups (n.s.). There was no statistically significant difference between the two groups in isokinetic dynamometric tests performed as 60° flexion, 60° extension, 180° flexion and 180° extension (n.s.).

CONCLUSION

The present study is the first that compared the clinical, radiological and functional results of the ST and DT techniques to date. Regardless of the number of the tunnels, similar results were obtained in ST and DT reconstruction using transpatellar tunnel technique.

LEVEL OF EVIDENCE

Level I.

Computational approach to correcting joint instability in patients with recurrent patellar dislocation

Patellar dislocation is a debilitating injury common in active adolescents and young adults. Conservative treatment after initial dislocation is often recommended, but almost half of these patients continue to suffer from recurrent dislocation. The objective of this study was to compare preoperative patellofemoral joint stability with stability after a series of simulated procedures, including restorative surgery to correct to pre-injury state, generic tibial tubercle osteotomy, patient-specific reconstructive surgery to correct anatomic abnormality, less invasive patient-specific surgery, and equivalent healthy controls. Three-dimensional, subject-specific finite element models of the patellofemoral joint were developed for 28 patients with recurrent patellar dislocation. A 50 N lateral load was applied to the patella to assess the lateral stability of the patellofemoral joint at 10° intervals from 0° to 40° flexion. Medial patellofemoral ligament reconstruction, along with reconstructive procedures to correct anatomic abnormality were simulated. Of all the simulations performed, the healthy equivalent control models showed the least patellar internal-external rotation, medial-lateral translation, and medial patellofemoral ligament restraining load during lateral loading tests. Isolated restorative medial patellofemoral ligament reconstruction was the surgery that resulted in the most patellar internal-external rotation, medial-lateral translation, and medial patellofemoral ligament reaction force across all flexion angles. Patient-specific reconstruction to correct anatomic abnormality was the only surgical group to have non-significantly different results compared with the healthy equivalent control group across all joint stability metrics evaluated. Statement of clinical significance: This study suggests patient-specific reconstructive surgery that corrects underlying anatomic abnormalities best reproduces the joint stability of an equivalent healthy control when compared with the pre-injury state, generic tibial tubercle osteotomy, and less invasive patient-specific surgery. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:768-776, 2020.

Autologous mesenchymal stem cell application for cartilage defect in recurrent patellar dislocation: A case report

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This is a novel management of a 21-year-old male with recurrent patellar dislocation.

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Fulkerson procedure was to realign the patella.

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Mesenchymal stem cell application was used for the articular cartilage defect.

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The outcome of this combination treatment was satisfying.

Introduction

Recurrent patellar dislocation can lead to articular cartilage injury. We report a 21-year old male with left patella instability and articular cartilage defect.

Presentation of case

A 21-year-old male presented with left patellar instability and pain. Knee range of motion (ROM) was limited when patella was dislocated (0–20°). The J-sign positive, patellar apprehension test was positive, with medial patella elasticity/patellar glide >2 quadrants. The Q angle, in the 90° flexed knee position was still normal. The plain radiograph imaging showed no abnormality. Insall-Salvati index was 1.12. The patient was diagnosed with recurrent patellar dislocation and cartilage lesion of the left knee, and was treated with combining Fulkerson osteotomy with the lateral retinacular release and percutaneous medial plication, followed by microfracture procedure and MSCs implantation.

Discussion

Recurrent patellar dislocation is uncommon problem while cartilage lesions following recurrent patellar dislocations are quite common, but still no consensus on the management.

Conclusion

Combination of Fulkerson osteotomy with the lateral retinacular release and percutaneous medial plication was effective in treating chronic patellar instability. The microfracture procedure and MSCs implantation was safe and could improve the cartilage regeneration in patients with articular cartilage defect due to recurrent patellar dislocation.

Patellofemoral instability in skeletally immature patients

Highlights

A decade after patellofemoral ligament reconstruction results remains satisfactory.It is a good option for patellar instability treatment in children.Patients with trochlear dysplasia benefit from trochleoplasty after physeal closure.

Background

Patellofemoral instability is a common cause of knee disability. Acute patellofemoral dislocation is the most common acute knee disorder in skeletally immature patients. In this group, the incidence of patellofemoral dislocation is approximately 43 per 100,000 individuals.

The precise objective addressed in the paper

Medial patellofemoral ligament (MPFL) reconstruction has a significant role in the treatment of patellofemoral instability in skeletally immature patients. We evaluated the medium and long-term results results of MPFL reconstruction as the sole method of patellofemoral instability treatment and their relationship with the presence of other potentially associated factors.

Methods

We conducted a prospective study with 35 young patients who underwent the same surgical technique between 2002 and 2009. Age, gender, patellar tilt, patella height, TT-TG, trochlear dysplasia, the Kujala score and the Tegner activity score were evaluated. Statistical analysis used SPSS^® 20.

Results

The mean age of the patients was 15.9 years. High patella was observed in 10% of patients. All patients had TT-TG within a normal range. Trochlear dysplasia was found in 80% of the patients: 40% had Dejour's type A; 34% type B; 20% type C and 6% type D. The medium-term Kujala score (84 ± 9) significantly improved compared to the pre-operative score (54 ± 11). However, a decline in the long-term (78 ± 3) score was observed. The Tegner activity score showed a significant decrease. The long-term results were significantly lower when patients had trochlear dysplasia type B to D.

Conclusions

A decade after isolated MPFL reconstruction, results remained satisfactory. Patients with trochlear dysplasia types B to D may benefit from associated trochleoplasty in a second intervention.

Computational analysis of factors contributing to patellar dislocation

Treatment for an initial incidence of patellar dislocation is usually conservative management; however, almost half of patients experience a subsequent, or multiple, dislocation(s). Patients often undergo multiple procedures which fail to treat the underlying anatomic abnormalities. The objective of this study was to evaluate interactions between key predisposing anatomic factors to patellar dislocation and identify combinations of abnormal factors which increase the risk of recurrent lateral dislocation. Four factors associated with lateral patellar dislocation were identified (sulcus angle, Insall-Salvati ratio, tibial tubercle-trochlear groove distance, and femoral anteversion). A finite element model of the patellofemoral joint was developed and parameterized so that a value for each factor could be applied and the model geometry/alignment would be modified accordingly. 100 combinations of the four factors were generated in separate computational simulations and resulting kinematics and forces of the patellofemoral joint were recorded. Sulcus angle was the most impactful factor on constraint. Multiple abnormal factors were generally required to produce the extremes of patellar alignment observed in this analysis. Understanding the underlying anatomic factors, and their effect on joint mechanics, for patients with recurrent lateral patellar dislocation will aid in determining optimal treatment pathways on a patient-specific basis.

Patellofemoral Pressure Changes After Static and Dynamic Medial Patellofemoral Ligament Reconstructions

BACKGROUND

Reconstructing the medial patellofemoral ligament (MPFL) has become a key procedure for stabilizing the patella. Different techniques to reconstruct the MPFL have been described: static techniques in which the graft is fixed rigidly to the bone or dynamic techniques with soft tissue fixation. Static MPFL reconstruction is most commonly used. However, dynamic reconstruction deforms more easily and presumably functions more like the native MPFL.

PURPOSE/HYPOTHESIS

The aim of the study was to evaluate the effect of the different MPFL fixation techniques on patellofemoral pressures compared with the native situation. The hypothesis was that dynamic reconstruction would result in patellofemoral pressures closer to those generated in an intact knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Seven fresh-frozen knee specimens were tested in an in vitro knee joint loading apparatus. Tekscan pressure-sensitive films fixed to the retropatellar cartilage measured mean patellofemoral and peak pressures, contact area, and location of the center of force (COF) at fixed flexion angles from 0° to 110°. Four different conditions were tested: intact, dynamic, partial dynamic, and static MPFL reconstruction. Data were analyzed using linear mixed models.

RESULTS

Static MPFL reconstruction resulted in higher peak and mean pressures from 60° to 110° of flexion (P < .001). There were no differences in pressure between the 2 different dynamic reconstructions and the intact situation (P > .05). The COF in the static reconstruction group moved more medially on the patella from 50° to 110° of flexion compared with the other conditions. The contact area showed no significant differences between the test conditions.

CONCLUSION

After static MPFL reconstruction, the patellofemoral pressures in flexion angles from 60° to 110° were 3 to 5 times higher than those in the intact situation. The pressures after dynamic MPFL reconstruction were similar as compared with those in the intact situation, and therefore, dynamic MPFL reconstruction could be a safer option than static reconstruction for stabilizing the patella.

CLINICAL RELEVANCE

This study showed that static MPFL reconstruction results in higher patellofemoral pressures and thus enhances the chance of osteoarthritis in the long term, while dynamic reconstruction results in more normal pressures.

The incidence of trochlear dysplasia in anterior cruciate ligament tears

PURPOSE

The purpose of the present epidemiologic study is to record the radiographic presence of trochlear dysplasia and patella alta in patients who undergo anterior cruciate ligament (ACL) reconstruction as a potential underlying factor for post-operative anterior knee pain (AKP).

METHODS

All consecutive cases of skeletally-mature ACL-deficient knees that would undergo ACL reconstruction in three different hospitals were prospectively included during a six-month period. Inclusion criteria were acute and sub-acute ACL injury with no previous ipsilateral knee operation. Patients with chronic ACL tears, prior-to-ACL-injury history of patellar instability or other PF disorders were excluded from the study.

RESULTS

A total of 299 knees were included (mean age 32 ± ten years). Forty-four (14.7 %) knees had a positive 'crossing sign' in the lateral X-rays and 255 (85.3 %) had no sign of trochlear dysplasia (p < 0.01). Among the cases with trochlear dysplasia, 41 (93 %) had type A trochlear dysplasia with the presence only of the 'crossing sign' and three (7 %) had type C trochlear dysplasia. Patellar height results included a mean Caton-Deschamps index of 1.0 ± 0.14 (0.5-1.4). Twenty (6.6 %) knees had an index of less than 0.8, and two (0.6 %) knees had an index less than 0.6. In contrast, 15 (5.0 %) knees had an abnormal value of more than 1.2, indicating patella alta.

CONCLUSIONS

The most important finding of the study is the increased prevalence of trochlear dysplasia and patella alta in patients with ACL injury, when compared to the incidence of trochlear dysplasia and patella alta in the general population in the literature. This finding could sound as an alert of a possible additional risk factor for post-operative anterior knee pain after ACL reconstruction.

Patellar dislocation due to iatrogenic quadriceps fibrosis: results of operative treatment in 54 cases

OBJECTIVE

To evaluate the clinical and functional results of a surgical treatment of patellar dislocation whose etiology was iatrogenic quadriceps fibrosis in children.

MATERIALS AND METHODS

A prospective study was undertaken from February 2004 to December 2009. The study included 54 pediatric patients (56 knees) that had developed dislocation of the patella after repeated intramuscular injections of antibiotic(s) into the quadriceps muscle. There were 11 males (20.4 %) and 43 females (79.6 %). The patients' mean age at surgery was 7 years, 9 months (range 6 years, 4 months to 12 years, 6 months). A complete history of each patient was recorded. The affected knees were evaluated preoperatively and postoperatively on the basis of the symptoms, signs, and roentgenographic findings. Patellar dislocation was classified according Bensahel's criteria. All patients had a three-part surgical procedure that combined capsulorrhaphy, quadricepsplasty, and transfer of the vastus medialis oblique to the superior border of the patella.

RESULTS

There has been no poor postsurgical result or recurrence so far; we have noted an ugly scar in nine knees (16.1 %), limitation of the knee flexion in five knees (8.9 %), and loss of extension of 5 °-20 ° in four knees (7.1 %). Overall, we attained excellent results in 39 knees (69.7 %), good results in 13 knees (23.2 %), and fair results in four knees (7.1 %).

CONCLUSION

In our cases of pediatric dislocation of the patella caused by iatrogenic quadriceps fibrosis, the introduced three-part surgical procedure has shown great success in restoring the realignment mechanism of the patella. The technique is simple, safe, and effective in skeletally immature children.

Treatment options for patellofemoral instability in sports traumatology

Patellofemoral instability not only involves lateral patellar dislocation, patellar mal-tracking or subluxation but can also cause a limiting disability for sports activities. Its underlying causes are known as morphological anomalies of the patellofemoral joint or the mechanical axis, femorotibial malrotation, variants of the knee extensor apparatus, and ligamentous insufficiencies often accompanied by poor proprioception. Athletes with such predisposing factors are either suffering from unspecific anterior knee pain or from slightly traumatic or recurrent lateral patellar dislocation Treatment options of patellar instability are vast, and need to be tailored individually depending on the athlete’s history, age, complaints and physical demands. Different conservative and surgical treatment options are reviewed and discussed, especially limited expectations after surgery.

Patellofemoral Instability: Evaluation by Magnetic Resonance Imaging

Objective

To determine the contribution of magnetic resonance imaging (MRI) in evaluating patelofemoral instability.

Methods

39 patients (45 knees) with patellar instability underwent knee magnetic resonance images between October 2009 and July 2011, at the Rede Lab's D’Or, in the city of Rio de Janeiro, State of Rio de Janeiro, were included. MRI were analyzed for the presence of bone, hyaline cartilage and soft-tissue abnormalities, as well as anatomic variants that may contribute to chronic patellar instability.

Results

The authors found, of the 45 knees analysed, bone changes in 44%, cartilaginous injuries in 64%, disruption of the medial patellofemoral ligament (MPFL) in 29% and joint morphology abnormalities in 73% patients. Meniscal tears were also identified in 2 (4%) patients and fibular fracture in one (2%) patient.

Conclusion

MRI allowed the detection of predisposing factors that may contribute to the development of patellofemoral instability and the diagnosis of bone, hyaline cartilage, ligamentous and meniscal abnormalities.

Medial patellofemoral ligament reconstruction - A novel technique

Patellofemoral instability is initially treated conservatively and surgical treatment is reserved for resistant cases. Reconstruction of medial patellofemoral ligament has gained popularity these days as it attempts at restoring soft tissue anatomy and biomechanics of medial patellar restraint back to normal. Here we describe our novel transverse patella single tunnel and femoral interference screw technique to reconstruct the medial patellofemoral ligament using free autologous gracilis and semitendinosus grafts.

Trochleoplasty and medial patellofemoral ligament reconstruction for recurrent patellar dislocation

We report a case of recurrent patellar dislocation with high-grade trochlear dysplasia which persisted despite two previous operations. We did a Dejour's sulcus deepening trochleoplasty, medial patellofemoral ligament reconstruction, and lateral retinacular release. Trochleoplasty and medial patellofemoral ligament reconstruction is required in patients with high grade trochlear dysplasia.

Reconstruction of medial patellofemoral ligament for chronic patellar instability

BACKGROUND

Disruption of the capsule, medial patellar retinaculum, and/or vastus medialis obliqus has been associated with recurrent patellar instability. Biomechanical studies have shown that the medial patellofemoral ligament (MPFL) is the main restraint against lateral patella displacement and reconstruction of the MPFL has become an accepted surgical technique to restore patellofemoral stability in patients having recurrent patellar dislocation. We report a prospective series of patients of chronic patellar instability treated by reconstruction of medial patellofemoral ligament.

MATERIALS AND METHODS

Twelve patients (15 knees) with recurrent dislocation of patella, were operated between January 2006 and December 2008. All patients had generalised ligament laxity with none had severe grade of patella alta or trochlear dysplasia. The MPFL was reconstructed with doubled semitendinosus tendon. Patients were followed up with subjective criteria, patellar inclination angle, and Kujala score.

RESULTS

The mean duration of followup after the operative procedures was an average of 42 months (range 24-60 months) 10 knees showed excellent results, 3 knees gave good results, and 2 knees had a fair result. The average patellar inclination angle decreased from 34.3° to 18.6°. The average preoperative Kujala functional score was 44.8 and the average postoperative score was 91.9.

CONCLUSION

MPFL reconstruction using the semitendinosus tendon gives good results in patients with chronic patellar instability without predisposing factors like severe patella alta and high-grade trochlear dysplasia, and for revision cases.

Dislocation/separation injuries among US high school athletes in 9 selected sports: 2005-2009

OBJECTIVE

To investigate the epidemiology of dislocations/separations in a nationally representative sample of high school student-athletes participating in 9 sports.

DESIGN

Descriptive epidemiologic study.

SETTING

Sports injury data for the 2005-2009 academic years were collected using an Internet-based injury surveillance system, Reporting Information Online (RIO).

PARTICIPANTS

A nationally representative sample of 100 US high schools.

ASSESSMENT OF RISK FACTORS

Injuries sustained as a function of sport and gender.

MAIN OUTCOME MEASURES

Dislocation/separation rates, body site, outcome, surgery, and mechanism.

RESULTS

Dislocations/separations represented 3.6% (n = 755) of all injuries. The most commonly injured body sites were the shoulder (54.9%), wrist/hand (16.5%), and knee (16.0%); 18.4% of dislocations/separations were recurrences of previous injuries at the same body site; 32.3% of injuries were severe (ie, student-athletes unable to return to play within 3 weeks of the injury date), and 11.8% required surgical repair. The most common mechanisms of injury were contact with another player (52.4%) and contact with the playing surface (26.4%). Injury rates varied by sport. In gender-comparable sports, few variations in patterns of injury existed. Rates were highest in football (2.10 per 10 000 athletic exposures) and wrestling (1.99) and lowest in baseball (0.24) and girls' soccer (0.27).

CONCLUSIONS

Although dislocation/separation injuries represent a relatively small proportion of all injuries sustained by high school student-athletes, the severity of these injuries indicates a need for enhanced injury prevention efforts. Developing effective targeted preventive measures depends on increasing our knowledge of dislocation/separation rates, patterns, and risk factors among high school athletes.

Bilateral rotational osteotomies of the proximal tibiae and tibial tuberosity distal transfers for the treatment of congenital lateral dislocations of patellae: a case report and literature review

Congenital dislocation of patella (CDP) causes varying degree of disability. Patients may present as late walkers with asymmetric gait, habitual or recurrent dislocators or even non-walkers if the condition is bilateral. Patellar instability is often associated with soft tissue or bony pathology. Soft tissue anomalies include lateral soft tissue contractures, shortened quadriceps as well as vastus medialis dysplasia (abnormal origin and insertion). Bony anomalies include shallow trochlear groove and hypoplastic patella or lateral femoral condyle. Soft tissue etiologies result in an imbalance of the dynamic forces acting on the patella while in bony etiologies the static stabilizers to resist lateral dislocation are compromised. External tibial torsion is an additional etiology, often under diagnosed due to the difficulty in measuring the Q angle of dislocated patella. We report a case of bilateral congenital lateral dislocations of the patellae treated with bilateral tibial rotational osteotomies with an 8 year and a 4 year follow up.