Tibial tubercle osteotomy: A biomechanical comparison of two techniques.

PURPOSE: The purpose of this study was to determine whether a modified step-cut tibial tubercle osteotomy (Maquet-Fulkerson hybrid) might produce comparable or better results than a standard oblique anteromedialization tibial tubercle osteotomy (Fulkerson type) and thus warrant the surgical need for additional cuts. METHODS: Six pairs of cadaveric knees were evaluated prior to and after tibial tubercle osteotomies. Simulation was done via a shallow knee bend simulator through 20 to 70° of knee flexion for the intact specimens and following the surgical procedures. The variables tested were trochlear contact forces and pressures and patellar motion. RESULTS: Testing showed a decreased force (P=0.027), peak contact pressure (P=0.01) and contact area (P=0.034) on the lateral trochlea of the femur for both types of osteotomies. There was no significant difference in the lateral femoral peak pressure or in the medial femoral peak pressure between the oblique cut and the step-cut. Also, there was no difference in patellar motion after either procedure. CONCLUSION: We conclude that both osteotomies decrease lateral patellofemoral trochlear pressure. The oblique osteotomy may decrease lateral pressure to a greater extent. Regarding biomechanical testing, there was no demonstrable advantage to performing a step-cut osteotomy.

Repair of lateral meniscus posterior horn detachment lesions: a biomechanical evaluation.

BACKGROUND: Posterior horn detachment (PHD) lesions of the lateral meniscus are commonly associated with acute anterior cruciate ligament (ACL) tears. Multiple surgeons have advocated for repair of this lesion at the time of ACL reconstruction. However, the biomechanical consequences of this lesion and its subsequent repair have not been evaluated. HYPOTHESIS: The PHD lesion of the lateral meniscus will lead to increased tibiofemoral contact pressures, and repair of this lesion to bone via a tibial tunnel can restore normal contact pressures during simulated gait. STUDY DESIGN: Controlled laboratory study. METHODS: Lateral compartment contact pressures were measured via a sensor on the tibial plateau in 8 cadaver knees with the knee intact, after sectioning the posterior horn of the lateral meniscus to simulate PHD, and after repairing the injury. The repair was performed using an ACL tunnel guide to drill a tunnel from the anteromedial tibia to the posterior horn attachment site. Dynamic pressure data were continuously collected using a conductive ink pressure sensing system while each knee was moved through a physiological gait flexion cycle. RESULTS: Posterior horn detachment caused a significant increase in tibiofemoral peak contact pressure from 2.8 MPa to 4.2 MPa (P = .03). After repair of the lesion to bone was performed through a transtibial tunnel, the peak contact pressure was 2.9 MPa. Posterior horn detachment also significantly decreased the maximum contact area over which tibiofemoral pressure is distributed from 451 mm(2) in the intact state to 304 mm(2) in the detached state. Repair of the PHD lesion increased the maximum contact area to 386 mm(2), however, this area was also significantly less than in the intact state (P = .05). CONCLUSION: Posterior horn detachment of the lateral meniscus causes increased peak tibiofemoral contact pressure. The peak pressure can be reduced to a normal level with repair of the lesion to bone via a transtibial tunnel. CLINICAL RELEVANCE: Posterior horn detachment of the lateral meniscus is a lesion often associated with an acute ACL tear. Debate exists concerning the importance of repairing PHD lesions at the time of ACL reconstruction. The data provided in this study may influence surgeons' management of the lesion.

Results of laboratory evaluation of acute knee effusion after anterior cruciate ligament reconstruction: what is found in patients with a noninfected, painful postoperative knee?

BACKGROUND: Infection after anterior cruciate ligament reconstruction is a rare and potentially devastating complication. No normative data have been reported for knee aspiration after anterior cruciate ligament reconstruction in the early postoperative period. HYPOTHESIS: Determining normative laboratory data from a retrospective review of noninfected early postoperative anterior cruciate ligament reconstruction knee effusions will allow for the calculation of an aspirate white blood cell (WBC) threshold value indicative of infection. STUDY DESIGN: Case series (diagnosis); Level of evidence, 4. METHODS: A 2-year retrospective chart review of 151 anterior cruciate ligament reconstruction patients was performed. Thirty-one noninfected patients meeting the inclusion and exclusion criteria and 1 infected patient had laboratory data collected, including peripheral blood and knee effusion aspirate analyses. Laboratory data from pertinent published studies of infected knees after anterior cruciate ligament reconstruction were combined with the data of our 1 infected patient, establishing a historical control group. Data were analyzed and results were then compared. Infected aspirate WBC threshold value statistics were then calculated. RESULTS: Analysis of noninfected knee effusion aspirates revealed a mean WBC count of 9600/uL (standard deviation [SD], 15 200), and a mean of 66% polymorphonuclear (PMN) cells (SD, 34). Aspirate WBC 98% confidence interval (CI) was 2800/uL to 16 200/uL, and the 98% CI for PMN cells was 58% to 84%. Aspirate WBC count >16 200/uL is 86% sensitive, 92% specific, and has a positive likelihood ratio of 10.4 as an indicator of infection. CONCLUSION: Benign effusion after anterior cruciate ligament reconstruction is common and is associated with elevated inflammatory markers. When concerned, knee aspiration after anterior cruciate ligament surgery gives the highest yield to differentiate between a painful effusion and a septic knee in the early postoperative period while awaiting definitive culture results. The authors report confidence intervals defining the range of cell count variables for noninfected patients requiring aspiration, specifically WBC and PMN, and suggest a WBC threshold value of >16 200/uL be used as an indicator of infection. On the basis of comparison with historical control data, the authors believe these data are significant and will be reliable for clinical use.

Knee medial compartment contact pressure increases with release of the type I anterior intermeniscal ligament.

BACKGROUND: The anterior intermeniscal ligament of the knee is at risk during knee arthroscopy, anterior cruciate ligament reconstruction, and tibial nail insertion. HYPOTHESIS: Release of the anterior intermeniscal ligament, in knees with type I ligaments, will result in altered contact pressures in the medial compartment. STUDY DESIGN: Controlled laboratory study. METHODS: Five fresh-frozen human cadaveric knees with intact type I anterior intermeniscal ligaments were chosen for testing in a modified MTS machine from 0 degrees to 60 degrees of flexion under 2 conditions: (1) intact and (2) after sharp sectioning of the anterior intermeniscal ligament. Measurements were made using inframeniscal contact pressure sensors covering the medial compartment. Poststudy analysis was done in 10 degrees increments between 0 degrees and 60 degrees of flexion, looking at peak contact pressure and the amount of contact area seeing pressure. RESULTS: Sectioning of the anterior intermeniscal ligament caused a statistically significant increase in the peak pressure at 20 degrees , 30 degrees , 40 degrees , and 50 degrees of knee flexion. The largest change occurred at 40 degrees of knee flexion, when the peak pressure increased by 27.5% (3.68 MPa to 4.69 MPa). Contact area decreased, although this difference was not statistically significant. CONCLUSION: Release of the anterior intermeniscal ligament results in increased peak contact pressures in the medial compartment of the knee. CLINICAL RELEVANCE: Care should be taken to avoid sacrifice of this ligament during surgery.