Evaluation of Differences in Patellar Height After Patellar Stabilization Procedures Not Intended to Address Patella Alta: A Multicenter Study.

Background: Recent studies have reported conflicting results as to whether isolated medial patellofemoral ligament reconstruction (MPFLr) leads to decreased patellar height. Purpose: To investigate if patellar stabilization surgery not intended to address patella alta influences patellar height. Study Design: Cohort study; Level of evidence, 3. Methods: A multicenter retrospective chart review was conducted, and patients who underwent MPFLr, medializing tibial tuberosity osteotomy (TTO), and/or trochleoplasty between 2016 and 2020 were included. The Caton-Deschamps index (CDI) was calculated from radiographs obtained preoperatively, 2 weeks postoperatively, and 3 months postoperatively. The preoperative CDI value was compared with the 2-week postoperative and 3-month postoperative values according to stabilization procedure (isolated MPFLr, isolated TTO, MPFLr + TTO, MPFLr + trochleoplasty, and MPFLr + trochleoplasty + TTO) using the paired t test. Analyses of the 1-bundle versus 2-bundle MPFLr technique and the presence of lateral retinacular release or lateral retinacular lengthening were conducted on the isolated MPFLr and combined MPFLr + TTO cohorts. Results: A total of 356 knees were included. Statistically significant pre- to postoperative decreases in CDI were seen in all stabilization procedures analyzed (P≤ .017 for all). Within the isolated MPFLr cohort, this significant decrease was seen at 2 weeks postoperatively with the 2-bundle technique (ΔCDI = -0.09; P < .001) but not with the 1-bundle technique (ΔCDI = -0.01; P = .621). Conclusion: The different surgical techniques analyzed in the current study affected patellar height, even when a distalizing TTO was not performed. The decrease was dependent on surgical technique, with a 2-bundle MPFLr leading to a statistically significant decrease and a 1-bundle MPFLr effecting no change.

Influence of tibial tuberosity position and trochlear depth on patellar tracking in patellar instability: Variations with Patella Alta.

BACKGROUND: Patella alta reduces articular constraints acting on the patella from the trochlear groove with the knee extended. The current study was performed to address how patella alta alters the influence of tibial tuberosity position and trochlear depth on patellar tracking in patients being treated for patellar instability. METHODS: Fifteen subjects with recurrent patellar instability participated in knee extension within a dynamic CT scanner. Computational models were reconstructed from the motions to characterize patellar lateral shift, patellar tilt, patellar height, trochlear depth and lateral position of the tibial tuberosity at 0° and 30° of knee flexion. Linear regressions were used to correlate patellar tracking with anatomy for an alta group (7 knees, Caton-Deschamps index > 1.2) and a non-alta group. FINDINGS: For the alta group, lateral patellar shift and tilt increased with increasing lateral position of the tibial tuberosity at 0° (r2 > 0.8, P < 0.005). For the non-alta group, lateral patellar shift and tilt increased as depth of the groove decreased at 0° (r2 > 0.8, P = 0.001). Lateral patellar tilt also increased with increasing lateral position of the tibial tuberosity at 30° for the non-alta group (r2 = 0.55, P = 0.04). INTERPRETATION: For patients with patellar instability, lateral patellar maltracking with the knee extended can be largely attributed to either a shallow trochlear groove or a combination of patella alta and a lateral position of the tibial tuberosity. These relationships should be considered in both conservative and surgical treatment planning.

Noniatrogenic Medial Patellar Dislocations: Case Series and International Patellofemoral Study Group Experience.

BACKGROUND: Most patellar dislocations occur in a lateral direction because of a summed lateral force vector and predisposing anatomic risk factors. Medial patellar instability is rare and is a well-recognized iatrogenic complication of an overly aggressive lateral retinacular release. Noniatrogenic medial patellar dislocations are rare. The management of these injuries is not well described. PURPOSE: To describe the experience of the International Patellofemoral Study Group with patients with noniatrogenic medial patellar dislocation. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Members of the International Patellofemoral Study Group (N = 64) were surveyed between October 2018 and April 2019. This group was chosen because of its wide referral base and interest in patellar instability. Specialists who had encountered a patient with medial patellar instability were sent a questionnaire inquiring about details of the case, including patient demographics, medical history, level of athletic competition, injury characteristics, and treatment. Cases were confirmed by physical examination records and, in some cases, with findings on advanced radiographic imaging. RESULTS: The survey response rate was 73% (47/64). Three of the 47 specialists (6.4%) reported they had seen a case of noniatrogenic medial patellar dislocation, for a total of 6 cases. Four cases were described as recurrent medial dislocations in the setting of hypermobile Ehlers-Danlos syndrome; 2 were treated nonoperatively, 1 underwent lateral patellofemoral ligament reconstruction, and 1 underwent derotational osteotomies. Two medial-sided patellar dislocations in collegiate athletes were sports-related injuries that required surgical debridement but no ligamentous reconstruction. None of the patients had persistent or recurrent instability at the time of their most recent follow-up. CONCLUSION: Noniatrogenic medial patellar dislocations are extremely rare. This case review suggests that the treatment of first-time medial patellar instability in patients without known risk factors should follow the same principles as the treatment of lateral instability with no known risk factors, which is nonoperative management. For patients with documented risk factors and recurrence, surgery to address the risk factors may be appropriate.

Factors Influencing Graft Function following MPFL Reconstruction: A Dynamic Simulation Study.

Medial patellofemoral ligament (MPFL) reconstruction is currently the primary surgical procedure for treating recurrent lateral patellar instability. The understanding of graft function has largely been based on studies performed with normal knees. The current study was performed to characterize graft function following MPFL reconstruction, focusing on the influence of pathologic anatomy on graft tension, variations with knee flexion, and the influence on patellar tracking. Knee squatting was simulated with 15 multibody dynamic simulation models representing knees being treated for recurrent lateral patellar instability. Squatting was simulated in a preoperative condition and following MPFL reconstruction with a hamstrings tendon graft set to allow 0.5 quadrants of lateral patellar translation with the knee at 30 degrees of flexion. Linear regressions were performed to relate maximum tension in the graft to parameters of knee anatomy. Repeated measures comparisons evaluated variations in patellar tracking at 5-degree increments of knee flexion. Maximum graft tension was significantly correlated with a parameter characterizing lateral position of the tibial tuberosity (maximum lateral tibial tuberosity to posterior cruciate ligament attachment distance, r 2 = 0.73, p < 0.001). No significant correlations were identified for parameters related to trochlear dysplasia (lateral trochlear inclination) or patella alta (Caton-Deschamps index and patellotrochlear index). Graft tension peaked at low flexion angles and was minimal by 30 degrees of flexion. MPFL reconstruction decreased lateral patellar shift (bisect offset index) compared with preoperative tracking at all flexion angles from 0 to 50 degrees of flexion, except 45 degrees. At 0 degrees, the average bisect offset index decreased from 0.81 for the preoperative condition to 0.71. The results indicate that tension within an MPFL graft increases with the lateral position of the tibial tuberosity. The graft tension peaks at low flexion angles and decreases lateral patellar maltracking. The factors that influence graft function following MPFL reconstruction need to be understood to limit patellar maltracking without overloading the graft or over constraining the patella.

Tibial tuberosity anteriomedialization vs. medial patellofemoral ligament reconstruction for treatment of patellar instability related to malalignment: Computational simulation.

BACKGROUND: Medial patellofemoral ligament reconstruction and tibial tuberosity anteromedialization are common treatment options for recurrent lateral patellar instability, although ligament reconstruction is not commonly applied to knees with lateral malalignment. METHODS: Multibody dynamic simulation was used to assess knee function following tibial tuberosity anteromedialization and medial patellofemoral ligament reconstruction for knees with lateral malalignment. Dual limb squatting was simulated with six models representing knees being treated for patellar instability with an elevated tibial tuberosity to trochlear groove distance. The patellar tendon attachment on the tibia was shifted medially (10 mm) and anteriorly (5 mm) to represent tibial tuberosity anteromedialization. A hamstrings tendon graft was represented for medial patellofemoral ligament reconstruction. Patellar tracking was quantified based on bisect offset index. The patellofemoral contact pressure distribution was quantified using discrete element analysis. Data were analyzed with repeated measures comparisons with post-hoc tests. FINDINGS: Both procedures significantly reduced bisect offset index, primarily at low flexion angles. The decrease was larger for tibial tuberosity anteromedialization, peaking at 0.18. Tibial tuberosity anteromedialization shifted contact pressures medially, significantly increasing the maximum medial contact pressure at multiple flexion angles, with the maximum pressure increasing up to 1 MPa. INTERPRETATION: The results indicate tibial tuberosity anteromedialization decreases lateral patellar maltracking more effectively than medial patellofemoral ligament reconstruction, but shifts contact pressure medially. Tibial tuberosity anteromedialization is likely to reduce the risk of post-operative instability compared to medial patellofemoral ligament reconstruction. The medial shift in the pressure distribution should be considered for knees with medial cartilage lesions, however.

A Primer on Running for the Orthopaedic Surgeon.

Long-distance running has become increasingly popular during the past decades. Many running patients pose questions to their orthopaedic surgeons regarding risks, benefits, and running techniques. This article identifies 11 running-related questions that patients may ask and provides information to help answer those questions. This review discusses data on the health benefits of running, common running injuries, the relationship between running and osteoarthritis, recommendations regarding running after orthopaedic surgery, running shoes, and other questions that may arise when treating the running athlete.

Anteroposterior distance between the tibial tuberosity and trochlear groove in patients with patellar instability.

BACKGROUND: Our objective was to describe a measurement to assess sagittal tibial tuberosity (TT)-trochlear groove (TG) distance and to compare this between asymptomatic (control) patients and patients with symptomatic patellar instability. METHODS: We compared static CT images of 22 fully extended knees of patients with symptomatic patellar instability with images of 22 asymptomatic knees. TT-TG distance was measured to quantify lateralization of the TT, and anteroposterior TT-TG distance was used to quantify the sagittal distance between these two points. Lateral trochlear inclination, sulcus angle, and trochlear depth were measured. Groups were compared using paired t tests (alpha = 0.05). Correlations of anteroposterior TT-TG distance with lateral trochlear inclination, sulcus angle, and trochlear depth were assessed using linear and multivariate regression. RESULTS: Mean TT-TG distances were 19.9 ±â€¯4.4 mm (symptomatic) and 16.8 ±â€¯5.5 mm (control) (mean ±â€¯std deviation) (P = 0.002). Mean anteroposterior TT-TG distances were 8.3 ±â€¯7.8 mm (symptomatic) and -0.5 ±â€¯4.6 mm (control) (P < 0.0001). The symptomatic group had greater measurements of trochlear dysplasia, with lower lateral trochlear inclination, greater sulcus angle, and lower trochlear depth (all P < 0.0001). Anteroposterior TT-TG distance and trochlear depth were strongly negatively correlated (r = 0.62, R2 = 0.39, P < 0.0001). CONCLUSIONS: In asymptomatic patients, the anteroposterior TT-TG distance was -0.5 mm, indicating that the TG and TT were nearly in the same coronal plane. In patients with symptomatic patellar instability, the TG was almost nine millimeters anterior, and this distance correlated with measurements of trochlear dysplasia. LEVEL OF EVIDENCE: III, case control study.

The Evolution of Patellofemoral Instability Surgery During the Past 25 Years.

Surgical treatment of patellofemoral instability has evolved during the past 25 years as we developed a better appreciation of anatomy and a more sophisticated understanding of pathophysiology. Currently, most patellofemoral surgeons use soft tissue procedures like medial patellofemoral ligament reconstruction to treat medial soft tissue insufficiency and tibial tuberosity or femoral osteotomy to correct substantial bony malalignment. Advances in imaging technology and computational analysis have allowed for more precise preoperative planning and outcome modeling so that the optimum operation using ≥1 of these procedures can be designed to meet the unique needs of an individual patient.

Dynamic tracking influenced by anatomy following medial patellofemoral ligament reconstruction: Computational simulation.

BACKGROUND: Continued patellar instability can occur following medial patellofemoral ligament (MPFL) reconstruction. Computational simulation of function was used to investigate the influence of the lateral position of the tibial tuberosity, trochlear dysplasia and patella alta on lateral patellar tracking following MPFL reconstruction. METHODS: Multibody dynamic simulation models were developed to represent nine knees being treated for recurrent patellar instability. Knee extension against gravity and dual limb squatting were simulated with and without simulated MPFL reconstruction. Graft resting lengths were set to allow 10mm and five millimeters of patellar lateral translation at 30° of knee flexion. The bisect offset index, lateral tibial tuberosity to posterior cruciate ligament tibial attachment (TT-PCL) distance, lateral trochlear inclination, and Caton-Deschamps index were quantified at every five degrees of knee flexion to characterize lateral tracking, lateral position of the tibial tuberosity, trochlear dysplasia, and patella alta, respectively. For the pre-operative and post-operative conditions and each type of motion, bisect offset index was correlated with the anatomical parameters using stepwise multivariate linear regression. RESULTS: For both motions, the pre-operative and post-operative bisect offset indices were significantly correlated with lateral trochlear inclination and lateral TT-PCL distance. For both motions, the adjusted r2 decreased with MPFL reconstruction, but was still approximately 0.5 for MPFL reconstruction allowing five millimeters of lateral translation. CONCLUSION: MPFL reconstruction decreases but does not eliminate lateral maltracking related to trochlear dysplasia and a lateralized tibial tuberosity. Patients with these pathologies are likely at the highest risk for instability related to maltracking following MPFL reconstruction.

Allowing one quadrant of patellar lateral translation during medial patellofemoral ligament reconstruction successfully limits maltracking without overconstraining the patella.

PURPOSE: Graft tensioning during medial patellofemoral ligament (MPFL) reconstruction typically allows for lateral patellar translation within the trochlear groove. Computational simulation was performed to relate the allowed patellar translation to patellofemoral kinematics and contact pressures. METHODS: Multibody dynamic simulation models were developed to represent nine knees with patellar instability. Dual limb squatting was simulated representing the pre-operative condition and simulated MPFL reconstruction. The graft was tensioned to allow 10, 5, and 0 mm of patellar lateral translation at 30° of knee flexion. The patellofemoral contact pressure distribution was quantified using discrete element analysis. RESULTS: For the 5 and 10 mm conditions, patellar lateral shift decreased significantly at 0° and 20°. The 0 mm condition significantly decreased lateral shift for nearly all flexion angles. All graft conditions significantly decreased lateral tilt at 0°, with additional significant decreases for the 5 and 0 mm conditions. The 0 mm condition significantly increased the maximum medial pressure at multiple flexion angles, increasing by 57% at 30°, but did not alter the maximum lateral pressure. CONCLUSIONS: Allowing 5 to 10 mm of patellar lateral translation limits lateral maltracking, thereby decreasing the risk of post-operative recurrent instability. Allowing no patellar translation during graft tensioning reduces maltracking further, but can overconstrain the patella, increasing the pressure applied to medial patellar cartilage already fibrillated or eroded from an instability episode.

Editorial Commentary: Measuring Coronal (Mal)Alignment for Patients With Patellar Instability: Tibial Tubercle-to-Trochlear Groove Versus Tibial Tubercle-to-Posterior Cruciate Ligament Distance.

Excessive lateralization of the tibial tuberosity is one of the anatomic factors that contribute to lateral patellar instability, which we usually correct surgically with tibial tuberosity osteotomy. Traditionally, coronal alignment was determined clinically by measuring the Q angle, which has proven to be unreliable. Radiographic measurements of coronal alignment made using computed tomography and magnetic resonance imaging are more reliable and have become the standard for determining the need for corrective tibial tuberosity osteotomy. However, measurements of the distance between the tibial tuberosity and the trochlear groove vary substantially according to the imaging modality, knee-flexion angle, and other factors. An alternative approach is to measure the distance between the tibial tuberosity and the posterior cruciate ligament, which negates the confounding influence of the knee-flexion angle. Controversy remains as to the optimum measurement technique. It is crucial that knee surgeons understand the nuances of the technique used to measure coronal alignment so they can choose the optimum surgery to achieve the desired anatomic correction.

When and How Far to Move the Tibial Tuberosity in Patients With Patellar Instability.

The many factors contributing to patellar instability have led to various surgical techniques that are used commonly today. When surgery is deemed necessary, the operation should be tailored to the patient's specific pathoanatomy. Patients with malalignment can often be stabilized by moving the tibial tuberosity to a more medial, anteromedial, or distal position. Subsequent changes in the forces acting on the patellofemoral joint will depend on the direction and distance of the tuberosity repositioning. When planning tuberosity osteotomies, it is crucial to understand how to use clinical and imaging modalities to measure and quantify tuberosity position accurately to achieve the desired degree of realignment.

Characterization of patellar maltracking using dynamic kinematic CT imaging in patients with patellar instability.

PURPOSE: Little has been reported on the relationship between patellar maltracking and instability. Patellar maltracking has been subjectively described with the "J sign" but is difficult to assess objectively using traditional imaging. Dynamic kinematic computed tomography (DKCT) allows dynamic assessment of the patellofemoral joint. DKCT was used to visualize and quantify patellar maltracking patterns, and severity of maltracking was correlated with the presence or absence of patellar instability symptoms. METHODS: Seventy-six knees in 38 patients were analysed using DKCT. Maltracking was defined as deviation of the patella from the trajectory of the trochlear groove and was characterized by patellar bisect offset, which was measured at 10° intervals of knee flexion during active flexion and extension. Bisect offset measurements were grouped by number of quadrants of maximum lateral patellar motion, with one, two, and three quadrants corresponding to 75-99, 100-125, and >125 %, respectively. Patellar instability symptoms were correlated with maltracking severity. RESULTS: Two knees were excluded because of poor imaging quality. Fifty of 74 knees had patellar instability, and 13 patients had bilateral symptoms. Of these, four (8 %) had normal tracking patterns; 41 (82 %) had increased lateral translation in extension, which we termed the J-sign pattern; 4 (8 %) had persistent lateralization of the patella throughout range of motion; and 1 had increased lateral translation in flexion. In knees with the J-sign pattern, degree of maltracking was graded by severity: J1 (n = 24), J2 (n = 19), and J3 (n = 15). The sensitivities of J-sign grades in predicting patellar instability symptoms were 50 % (J1), 80 % (J2), and 93 % (J3) (p < 0.01). There were significant differences in sensitivity between knees with no J sign or J1 versus J2 or J3 (p = 0.02). CONCLUSION: DKCT showed several patellar maltracking patterns in patients with patellar instability. A J-sign pattern with more than two quadrants of lateral translation correlated with the presence of patellar instability symptoms. Incorporation of this approach of objectively quantifying maltracking patterns is recommended in the evaluation of patellofemoral instability. LEVEL OF EVIDENCE: IV.

Dynamic tracking influenced by anatomy in patellar instability.

BACKGROUND: The current study was performed to correlate anatomical parameters related to trochlear dysplasia, tibial tuberosity position, and patella alta with in vivo patellar tracking for subjects with recurrent patellar instability. METHODS: Eight subjects with recurrent patellar instability that failed conservative treatment were evaluated using computational reconstruction of in vivo knee motion. Computational models were created from dynamic CT scans of the knee during extension against gravity. Shape matching techniques were utilized to position a single model of each bone (femur, patella and tibia) to represent multiple positions of knee extension. Patellar tracking was characterized by the bisect offset index (lateral shift) and lateral tilt. Anatomical parameters were characterized by the inclination of the lateral ridge of the trochlear groove, the lateral distance from the tibial tuberosity to the posterior cruciate ligament attachment (lateral TT-PCL distance), and the Caton-Deschamps index. Stepwise multivariable linear regression analysis was used to relate patellar tracking to the anatomical parameters at low (<20°) and high flexion angles. RESULTS: At low flexion angles, both lateral trochlear inclination and lateral TT-PCL distance were significantly correlated with bisect offset index (p=0.02). Only lateral trochlear inclination was significantly correlated with lateral tilt (p<0.001). At high flexion angles, bisect offset index and lateral tilt were correlated with only lateral TT-PCL distance (p≤0.02). CONCLUSION: Parameters related to trochlear dysplasia and tibial tuberosity position were both related to patellar tracking, but the relationship changed with the flexion angle. CLINICAL RELEVANCE: The anatomical parameters related to patellar tracking can be used to evaluate the risk of continued instability and guide surgical treatment.

The Relationship Between Tibial Tuberosity-Trochlear Groove Distance and Abnormal Patellar Tracking in Patients With Unilateral Patellar Instability.

PURPOSE: To evaluate the role of tibial tuberosity-trochlear groove (TT-TG) distance in patellofemoral kinematics by retrospectively reviewing the dynamic computed tomography scans of patients with unilateral patellofemoral instability and comparing unstable and contralateral asymptomatic knees. METHODS: We reviewed all dynamic computed tomography scans obtained at one tertiary care hospital from 2008 through 2013 and identified 25 patients with a history of recurrent unilateral patellofemoral instability. During the scans, subjects performed active knee extension against gravity. Both knees were imaged simultaneously. Lateral patellar tilt (LPT) and bisect offset (BO) were measured to assess tracking. TT-TG distance was measured to assess alignment. Measurements were made in full extension, maximum flexion, and approximately 10° increments in between. The significance level was set at P < .05. RESULTS: LPT, BO, and TT-TG distance were highest in extension and decreased with flexion. Measurements were higher in symptomatic than in asymptomatic knees, with significant differences identified for LPT, BO, and TT-TG distance at 5° and 15° and for TT-TG distance at 25° and 35° (P < .05). TT-TG distance was associated with LPT and BO, with r(2) values in symptomatic knees of 0.55 for TT-TG distance and LPT and of 0.45 for TT-TG distance and BO. CONCLUSIONS: In patients with unilateral patellar instability, LPT, BO, and TT-TG distance are higher on the unstable side. An association exists between TT-TG distance and the tracking parameters studied, suggesting that TT-TG distance relates to patellar tracking, and a laterally positioned tibial tuberosity may predispose to instability episodes. LEVEL OF EVIDENCE: Level IV, diagnostic study.

Correlation Between Changes in Tibial Tuberosity-Trochlear Groove Distance and Patellar Position During Active Knee Extension on Dynamic Kinematic Computed Tomographic Imaging.

PURPOSE: The purpose of this study was to evaluate changes in tibial tuberosity-trochlear groove (TTTG) distance with knee flexion in patients with patellar instability and correlate it with patellar position. METHODS: Patients with symptomatic patellar instability underwent dynamic kinematic computed tomography (CT) during a cycle of knee extension from flexion. Knee flexion angles and corresponding TTTG distances, bisect offset, and patellar tilt were measured. Of the 51 knees, 37 had data available for interpolation between 5° and 30°. Results were interpolated to standardized intervals between 5° and 30° of knee flexion. Repeated-measures analysis (to identify differences between TTTG measurements at various knee flexion angles) and linear regression models (to assess for correlations between TTTG distance and bisect offset and between TTTG distance and patellar tilt) were used. RESULTS: Fifty-one symptomatic knees in 38 patients were available for analysis. Bisect offset and patellar tilt correlated significantly (P < .001) with TTTG distance over all flexion angles. Interpolated results for comparison resulted in 37 knees in which the mean TTTG distance of 17.2 ± 5.8 mm at 5° decreased to 15.5 ± 5.7, 13.0 ± 5.5, and 11.5 ± 4.9 mm at 10°, 20°, and 30° of knee flexion, respectively. Mean TTTG at 5° was 1.5 times greater than that at 30° (P < .001). At 5°, 70.3% (26 of 37) of knees had a TTTG distance of more than 15 mm; at 30°, only 24.3% (9 of 37) exceeded this threshold. CONCLUSIONS: Knee flexion angle during imaging is a critical factor when measuring TTTG distance to evaluate patellofemoral instability. We found that the mean TTTG distance varied by 5.7 mm between 5° and 30° of flexion in patients with symptomatic instability, although this relationship was not completely linear. Bisect offset and patellar tilt measurements mirrored this pattern, suggesting that TTTG distance influences patellar tracking in these patients. LEVEL OF EVIDENCE: Level IV, prognostic case series.

Variations in kinematics and function following patellar stabilization including tibial tuberosity realignment.

PURPOSE: The current study was performed to characterize the influence of patellar stabilization procedures on patellofemoral and tibiofemoral dynamic motion. METHODS: Six knees were evaluated pre-operatively and 1 year or longer following stabilization via tibial tuberosity realignment, with simultaneous medial patellofemoral ligament reconstruction performed for five knees. Knees were imaged during extension against gravity using a dynamic CT scanner. Models representing each knee at several positions of extension were reconstructed from the images. Local coordinate systems were created within one femur, patella and tibia for each knee, with shape matching of the bones used to transfer the coordinate axes to the other models. The patellar lateral shift and tilt and tibial external rotation were quantified based on the reference axes and interpolated to flexion angles from 5° to 40°. Pre-operative and post-operative data were compared with the paired t tests. RESULTS: Surgical realignment significantly decreased the average patellar lateral shift and tilt at low flexion angles. At 5°, surgical realignment decreased the average lateral shift from 15.5 (6.3) to 8.5 (4.7) mm and decreased the average lateral tilt from 20.8 (9.4)° to 13.8 (6.4)°. The changes were statistically significant (p<0.05) at 5° and 10° of flexion, as well as 20° for lateral shift. The average tibial external rotation also increased significantly at 30° and 40° following surgery. CONCLUSION: Patellar stabilization including a component of tuberosity realignment reduces patellar lateral shift and tilt at low flexion angles, but the long-term influence of increased tibial external rotation on tibiofemoral function is currently unknown. LEVEL OF EVIDENCE: Prospective comparative study, Level II.

The Arthroscopic Surgical Skill Evaluation Tool (ASSET).

BACKGROUND: Surgeries employing arthroscopic techniques are among the most commonly performed in orthopaedic clinical practice; however, valid and reliable methods of assessing the arthroscopic skill of orthopaedic surgeons are lacking. HYPOTHESIS: The Arthroscopic Surgery Skill Evaluation Tool (ASSET) will demonstrate content validity, concurrent criterion-oriented validity, and reliability when used to assess the technical ability of surgeons performing diagnostic knee arthroscopic surgery on cadaveric specimens. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Content validity was determined by a group of 7 experts using the Delphi method. Intra-articular performance of a right and left diagnostic knee arthroscopic procedure was recorded for 28 residents and 2 sports medicine fellowship-trained attending surgeons. Surgeon performance was assessed by 2 blinded raters using the ASSET. Concurrent criterion-oriented validity, interrater reliability, and test-retest reliability were evaluated. RESULTS: Content validity: The content development group identified 8 arthroscopic skill domains to evaluate using the ASSET. Concurrent criterion-oriented validity: Significant differences in the total ASSET score (P < .05) between novice, intermediate, and advanced experience groups were identified. Interrater reliability: The ASSET scores assigned by each rater were strongly correlated (r = 0.91, P < .01), and the intraclass correlation coefficient between raters for the total ASSET score was 0.90. Test-retest reliability: There was a significant correlation between ASSET scores for both procedures attempted by each surgeon (r = 0.79, P < .01). CONCLUSION: The ASSET appears to be a useful, valid, and reliable method for assessing surgeon performance of diagnostic knee arthroscopic surgery in cadaveric specimens. Studies are ongoing to determine its generalizability to other procedures as well as to the live operating room and other simulated environments.

Complications of medial patellofemoral ligament reconstruction: common technical errors and factors for success: AAOS exhibit selection.

BACKGROUND: The role of medial patellofemoral ligament reconstruction in reestablishing patellofemoral joint stability has recently been reported with increasing frequency. The purpose of this study was to review the reported complications of medial patellofemoral ligament reconstruction, highlight the common technical errors, and discuss the potential complications that can arise from this procedure. METHODS: We review the literature on medial patellofemoral ligament reconstruction, including the reported causes of failure. In addition, we present three cases and discuss the multiple factors that are crucial for success, including patient selection, tunnel placement, graft isometry, and determination of the need for concurrent realignment surgery. RESULTS: The principles of surgical management require a thorough understanding of proper patient selection and of the interaction between the roles of the osseous and soft-tissue restraints on the patella. Creating a logical treatment algorithm based on pathoanatomy can elucidate the need for concurrent distal realignment procedures. Tunnel positioning is critical in recreating appropriate patellofemoral alignment. The reported complications include patellofemoral arthrosis, graft impingement, and graft failure. CONCLUSIONS: Many of the complications that can arise from medial patellofemoral ligament reconstruction are the result of technical error and can be avoided by understanding the potential complications associated with this procedure.

The effect of tibial tuberosity realignment procedures on the patellofemoral pressure distribution.

PURPOSE: The study was performed to characterize the influence of tibial tuberosity realignment on the pressure applied to cartilage on the patella in the intact condition and with lesions on the lateral and medial facets. METHODS: Ten knees were loaded in vitro through the quadriceps (586 N) and hamstrings (200 N) at 40°, 60°, and 80° of flexion while measuring patellofemoral contact pressures with a pressure sensor. The tibial tuberosity was positioned 5 mm lateral of the normal position to represent lateral malalignment, 5 mm medial of the normal position to represent tuberosity medialization, and 10 mm anterior of the medial position to represent tuberosity anteromedialization. The knees were tested with intact cartilage, with a 12-mm-diameter lesion created within the lateral patellar cartilage, and with the lateral lesion repaired with silicone combined with a medial lesion. A repeated measures ANOVA and post hoc tests were used to identify significant (P < 0.05) differences in the maximum lateral and medial pressure between the tuberosity positions. RESULTS: Tuberosity medialization and anteromedialization significantly decreased the maximum lateral pressure by approximately 15% at 60° and 80° for intact cartilage and cartilage with a lateral lesion. Tuberosity medialization significantly increased the maximum medial pressure for intact cartilage at 80°, but the maximum medial pressure did not exceed the maximum lateral pressure for any testing condition. CONCLUSIONS: The results indicate that medializing the tibial tuberosity by 10 mm reduces the pressure applied to lateral patellar cartilage for intact cartilage and cartilage with lateral lesions, but does not overload medial cartilage.