The effect of axial rotation of the anterior resection plane in patellofemoral arthroplasty.

BACKGROUND: Patellofemoral arthroplasty (PFA) has a small but definite place in replacement surgery of the knee, especially in young patients. The main surgical considerations in PFA are the patient's anatomy, the type of prosthesis and the surgical technique. The surgical technique and PFA success rely heavily on the anterior resection. In this study we investigate the effect of axial rotation of the anterior resection plane. METHODS: We tested the outcome of PFA fit based on resection footprint measurements, axial and coronal groove angles, and lateral trochlear inclination (LTI) angle in a virtual PFA model. The range of anterior resection plane axial rotations was from five degree internal to five degree external with an increment of one degree. RESULTS: Axial rotation of anterior resection plane changes the resection footprint dimension, which leads to coronal rotation of the femoral component. External rotation of the resection plane results in valgus rotation of the trochlear groove and decreased LTI after PFA and the opposite was observed for internal rotation. CONCLUSION: Our study showed that by changing the axial rotation of the anterior cut, the coronal groove of the prosthesis can be altered to lie more closely with the native groove line without compromising the prosthesis-cartilage transition.

Development of a patient-specific femoral component for unicompartmental knee replacement.

This study describes the development of a novel, patient-specific unicompartmental knee prosthesis. The geometries of the lateral and medial condyles are approximated by polynomials, instead of single radius circles that are commonly used. Furthermore, a database containing the geometries of healthy knees is used to generate appropriate knee geometries according to certain measurements of the unhealthy knee. This new method enables a customized design of a unicompartmental knee replacement that will closely resemble the articulating surfaces of the normal, healthy knee joint.

A preliminary study of patellar tendon torques during jumping.

The etiology of patellar tendinopathy (jumper's knee) has been attributed to a significant increase in patellar tendon torques associated with jumping. While some investigators have suggested that patellar tendon torques are greater during takeoff, little is known about the relative magnitudes of patellar tendon torques during takeoff and landing. We hypothesized that peak patellar tendon torques are greater in jump takeoff than in landing, and that there is a linear correlation between jump height and peak patellar tendon torque. Seven asymptomatic, recreational male athletes each performed a series of 21 jumps ranging from low to maximal height. A calibrated fiber-optic sensor, implanted transversely within the patellar tendon was used to measure the knee torque during takeoff and landing. There was no significant difference in the peak patellar tendon torque experienced during takeoff and landing within individuals. There was a moderate correlation (r = .64) between maximum takeoff patellar tendon torques and jump height. There was a weak correlation (r = .52) between maximum landing patellar tendon torques and jump height. There was a moderate correlation (r = .67) between maximum 60 degrees/s isokinetic extension torque and maximum jump height. The lack of a strong correlation between jump height and patellar tendon forces during take-off or landing suggests that these forces may be technique dependent. Therefore, modifying takeoff and/or landing techniques could reduce patellar tendon force and potentially lessen the incidence of patellar tendinopathy.

[The medial patellofemoral ligament: function, injury, and treatment]. / Das mediale patellofemorale Ligament : Funktion, Verletzung und Therapie.

The medial patellofemoral ligament or MPFL is the prime soft tissue stabilizer of the patella. The MPFL is a non-isometric ligament lying in the second fascial layer of the knee; it is tight in extension and lax in flexion. The ligament is always torn in acute patellar dislocations. As "form follows function" we believe that the MPFL should be reconstructed in such a way that it stabilizes the patella without changing its movement pattern.

Goodness-of-fit determination of femoral knee prosthesis using computer segmentation.

35 patients undergoing Total Knee Arthroplasty (TKA) were examined with Computerized Tomography (CT). 3D computer models were created through segmentation of the CT scan data with Materialize MIMICS. Morphological dimensions of ten selected parameters were measured and then compared to two commercial femoral prosthesis design ranges. All measuring techniques were validated and the reproducibility of measuring morphological dimensions with points and planes from landmarks were investigated. The chi2 test was used as a goodness-of-fit parameter to determine which femoral component would achieve the best geometric fit for a specific patient. After establishing a database of geometric values, the method can be used to calculate the dimensions of a customized femoral knee prosthesis to achieve a perfect geometric fit for a TKA patient.

Endocrine and immune effects of dexamethasone in unilateral total knee replacement.

The effect of acute pre-surgery dexamethasone treatment on the inflammatory immune and endocrine responses to orthopaedic surgery was investigated. Whole blood samples were obtained before and 5 days after surgery for immune analysis, and serum was obtained before and 6 h, 3 days and 5 days after surgery for endocrine assessment. Dexamethasone did not affect the post-surgery granulocyte response, but inhibited the increase in monocyte count (an average increase of 38.5% was seen in the control group). Peak C-reactive protein concentration (3 days after surgery) was 51.4% lower in the dexamethasone group than in the control group. Dexamethasone had a major effect on cortisol concentrations and the cortisol:testosterone and cortisol:dehydroepiandrosterone ratios, but no effect on anabolic hormone concentrations. In conclusion, acute pre-surgery dexamethasone treatment may have beneficial effects in the post-surgery period, by limiting the extent of systemic inflammation and the cortisol response.