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Tibial Tuberosity-Trochlear Groove Distance and Patellar Tracking in Symptomatic and Asymptomatic knees in Patients with Unilateral Patellofemoral Instability
ABSTRACTS
reported as averages. MPFL strength of 208N was used as the control, as documented in the literature. The widths of all patellas were measured. Utilizing these measurements, we could quantify the force necessary for 50% patellar displacement (subluxation) and 100% patellar displacement (dislocation). Additionally, we examined the peak force to fixation failure for all methods. 100% patellar displacement or fixation failure, whichever occurred first, was considered failure. Method of failure was also examined. Results: Three forms of reconstruction required force >208N for 100% patellar displacement (dislocation) and fixation failure; suspensory cortical fixation patella and femur, suspensory cortical fixation patella interference screw femur, and interference screw patella suspensory cortical fixation femur. All methods of reconstruction required <208N for 50% patellar displacement (subluxation). All methods of MPFL reconstruction when compared against each other and the native strength of the MPFL, 208N, demonstrated significantly different strengths when examined for 50% and 100% displacement of the patella as well as peak force to displacement (F ¼ 8.4, F crit ¼ 2.3 (results of ANOVA); p<0.00001)). All methods of fixation employing an interference screw failed secondary to graft pullout at the interference screw. Methods employing suture anchors and two suspensory cortical fixations failed at the graft-suture anastomosis. No reconstruction method failure violated the integrity of the human gracilis allograft. Conclusion: This is the first MPFL reconstruction biomechanical study to examine the strength of fixation utilizing suspensory cortical fixation in matched pair human cadavers with human gracilis allografts. Three methods of reconstruction were stronger than the native MPFL, 208N, with the strongest method of MPFL reconstruction being interference screw patella suspensory cortical fixation femur; 233.9N and 267.1N for 100% patellar displacement and peak to force failure, respectively. Additionally, our analysis demonstrates that human gracilis allograft can withstand forces far greater than the native MPFL, 208N; therefore, suggesting human gracilis allograft as an acceptable tissue alternative for MPFL reconstruction. Tibial Tuberosity-Trochlear Groove Distance and Patellar Tracking in Symptomatic and Asymptomatic knees in Patients with Unilateral Patellofemoral Instability SS-28 Thursday, May 1, 5:55 PM ARIEL WILLIAMS, M.D., PRESENTING AUTHOR JOHN ELIAS, PH.D. MIHO TANAKA, M.D. SHADPOUR DEMEHRI, M.D. GAURAV THAWAIT, M.D. JOHN CARRINO, M.D., M.P.H. ANDREW COSGAREA, M.D. Introduction: Recurrent patellofemoral instability is a relatively uncommon problem. Its etiology is variable, making determining the best treatment challenging. Various imaging modalities are used to determine the optimal surgical technique, and a number of radiographic
e15
measures are employed. Radiographically, patellofemoral instability has been associated with abnormal indicators of patellar tracking, including an elevated patellar tilt (PT) and bisect offset (BO). It has also been associated with abnormal bony anatomy, as measured by the tibial tuberosity-trochlear groove distance (TTTG). However, the relationship between these parameters and how they change with knee motion is not clear. Our objective was to use dynamic CT imaging to compare PT, BO, and TTTG in knees with and without symptoms of patellofemoral instability. We hypothesized that PT, BO, and TTTG would vary with knee motion and that TTTG would influence both PT and BO. Methods: All dynamic CT scans performed at our institution for the evaluation of patellofemoral instability were reviewed. During the scans, subjects performed active knee extension against gravity. Images were obtained of both knees at 0.5 second intervals. Starting in full knee extension and repeating measurements in approximately 10 degree increments, PT, BO, and TTTG were measured for each knee. Charts were then reviewed to determine surgical history, whether the patients’ symptoms were bilateral or unilateral, and, in cases of unilateral symptoms, which knee was affected. Patients with bilateral symptoms or a history of patellar-stabilizing surgery were excluded from the analysis. T-tests were used to compare PT, BO, and TTTG between symptomatic and asymptomatic knees at each flexion angle. Linear regressions were performed to determine the relationships between radiographic parameters. The criteria for significance was set as p0.05. Results: 38 scans were reviewed. Symptoms were unilateral in 25 patients. Of these patients, 9 had had patellar-stabilizing surgery in the past and so were excluded. Comparing symptomatic and asymptomatic knees, PT, BO, and TTTG were higher in symptomatic knees. These differences were significant for PT at 0 degrees, BO at 0 degrees, and TTTG at 0, 10, and 20 degrees. PT, BO, and TTTG all decreased with increasing flexion angle. R-squared values for TTTG and PT were 0.64 in symptomatic knees and 0.55 in asymptomatic knees. Rsquared values for TTTG and BO were 0.57 in symptomatic knees and 0.51 in asymptomatic knees. Conclusion: Differences in both tracking and anatomic alignment were observed between knees with and without symptoms of patellofemoral instability. Radiographic measures of tracking and alignment changed with knee motion and, in knees with instability symptoms, were most abnormal at lower flexion angles. TTTG had a measurable influence on tracking in all knees, although the affect was more pronounced in those with instability symptoms. Together, these findings suggest that maltracking and malalignment play important and interrelated roles in patellofemoral instability.
Long-Term Outcomes of Arthroscopic Revision Rotator Cuff Repair: Clinical Outcomes of SingleRow Arthroscopic Revision Rotator Cuff Repair SS-29 Friday, May 2, 9:45 AM WESLEY NOTTAGE, M.D., PRESENTING AUTHOR JASON JANCOSKO, D.O., M.P.T.
reported as averages. MPFL strength of 208N was used as the control, as documented in the literature. The widths of all patellas were measured. Utilizing these measurements, we could quantify the force necessary for 50% patellar displacement (subluxation) and 100% patellar displacement (dislocation). Additionally, we examined the peak force to fixation failure for all methods. 100% patellar displacement or fixation failure, whichever occurred first, was considered failure. Method of failure was also examined. Results: Three forms of reconstruction required force >208N for 100% patellar displacement (dislocation) and fixation failure; suspensory cortical fixation patella and femur, suspensory cortical fixation patella interference screw femur, and interference screw patella suspensory cortical fixation femur. All methods of reconstruction required <208N for 50% patellar displacement (subluxation). All methods of MPFL reconstruction when compared against each other and the native strength of the MPFL, 208N, demonstrated significantly different strengths when examined for 50% and 100% displacement of the patella as well as peak force to displacement (F ¼ 8.4, F crit ¼ 2.3 (results of ANOVA); p<0.00001)). All methods of fixation employing an interference screw failed secondary to graft pullout at the interference screw. Methods employing suture anchors and two suspensory cortical fixations failed at the graft-suture anastomosis. No reconstruction method failure violated the integrity of the human gracilis allograft. Conclusion: This is the first MPFL reconstruction biomechanical study to examine the strength of fixation utilizing suspensory cortical fixation in matched pair human cadavers with human gracilis allografts. Three methods of reconstruction were stronger than the native MPFL, 208N, with the strongest method of MPFL reconstruction being interference screw patella suspensory cortical fixation femur; 233.9N and 267.1N for 100% patellar displacement and peak to force failure, respectively. Additionally, our analysis demonstrates that human gracilis allograft can withstand forces far greater than the native MPFL, 208N; therefore, suggesting human gracilis allograft as an acceptable tissue alternative for MPFL reconstruction. Tibial Tuberosity-Trochlear Groove Distance and Patellar Tracking in Symptomatic and Asymptomatic knees in Patients with Unilateral Patellofemoral Instability SS-28 Thursday, May 1, 5:55 PM ARIEL WILLIAMS, M.D., PRESENTING AUTHOR JOHN ELIAS, PH.D. MIHO TANAKA, M.D. SHADPOUR DEMEHRI, M.D. GAURAV THAWAIT, M.D. JOHN CARRINO, M.D., M.P.H. ANDREW COSGAREA, M.D. Introduction: Recurrent patellofemoral instability is a relatively uncommon problem. Its etiology is variable, making determining the best treatment challenging. Various imaging modalities are used to determine the optimal surgical technique, and a number of radiographic
e15
measures are employed. Radiographically, patellofemoral instability has been associated with abnormal indicators of patellar tracking, including an elevated patellar tilt (PT) and bisect offset (BO). It has also been associated with abnormal bony anatomy, as measured by the tibial tuberosity-trochlear groove distance (TTTG). However, the relationship between these parameters and how they change with knee motion is not clear. Our objective was to use dynamic CT imaging to compare PT, BO, and TTTG in knees with and without symptoms of patellofemoral instability. We hypothesized that PT, BO, and TTTG would vary with knee motion and that TTTG would influence both PT and BO. Methods: All dynamic CT scans performed at our institution for the evaluation of patellofemoral instability were reviewed. During the scans, subjects performed active knee extension against gravity. Images were obtained of both knees at 0.5 second intervals. Starting in full knee extension and repeating measurements in approximately 10 degree increments, PT, BO, and TTTG were measured for each knee. Charts were then reviewed to determine surgical history, whether the patients’ symptoms were bilateral or unilateral, and, in cases of unilateral symptoms, which knee was affected. Patients with bilateral symptoms or a history of patellar-stabilizing surgery were excluded from the analysis. T-tests were used to compare PT, BO, and TTTG between symptomatic and asymptomatic knees at each flexion angle. Linear regressions were performed to determine the relationships between radiographic parameters. The criteria for significance was set as p0.05. Results: 38 scans were reviewed. Symptoms were unilateral in 25 patients. Of these patients, 9 had had patellar-stabilizing surgery in the past and so were excluded. Comparing symptomatic and asymptomatic knees, PT, BO, and TTTG were higher in symptomatic knees. These differences were significant for PT at 0 degrees, BO at 0 degrees, and TTTG at 0, 10, and 20 degrees. PT, BO, and TTTG all decreased with increasing flexion angle. R-squared values for TTTG and PT were 0.64 in symptomatic knees and 0.55 in asymptomatic knees. Rsquared values for TTTG and BO were 0.57 in symptomatic knees and 0.51 in asymptomatic knees. Conclusion: Differences in both tracking and anatomic alignment were observed between knees with and without symptoms of patellofemoral instability. Radiographic measures of tracking and alignment changed with knee motion and, in knees with instability symptoms, were most abnormal at lower flexion angles. TTTG had a measurable influence on tracking in all knees, although the affect was more pronounced in those with instability symptoms. Together, these findings suggest that maltracking and malalignment play important and interrelated roles in patellofemoral instability.
Long-Term Outcomes of Arthroscopic Revision Rotator Cuff Repair: Clinical Outcomes of SingleRow Arthroscopic Revision Rotator Cuff Repair SS-29 Friday, May 2, 9:45 AM WESLEY NOTTAGE, M.D., PRESENTING AUTHOR JASON JANCOSKO, D.O., M.P.T.