Summary Objective To test the hypothesis that individuals with patellofemoral pain (PFP) exhibit greater patellofemoral joint stress profiles compared to persons who are pain-free. Methods Ten females with PFP and ten gender, age, and activity-matched pain-free controls participated. Patella and femur stress profiles were quantified utilizing subject-specific finite element (FE) models of the patellofemoral joint at 15° and 45° of knee flexion. Input parameters for the FE model included: (1) joint geometry, (2) quadriceps muscle forces, and (3) weight-bearing patellofemoral joint kinematics. Using a nonlinear FE solver, quasi-static loading simulations were performed to quantify each subject’s patellofemoral joint stress profile during a static squatting maneuver. The patella and femur peak and mean hydrostatic pressure as well as the peak and mean octahedral shear stress for the elements representing the chondro-osseous interface were quantified. Results Compared to the pain-free controls, individuals with PFP consistently exhibited greater peak and mean hydrostatic pressure as well as peak and mean octahedral shear stress for the elements representing the patella and femur chondro-osseous interface across the two knee flexion angles tested (15° and 45°). Conclusions The combined finding of elevated hydrostatic pressure and octahedral shear stress across the two kneeflexion angles supports the premise that PFPmay be associated with elevated joint stress. Therefore, treatments aimed at decreasing patellofemoral joint stress may be indicated in this patient population.

As an integral part of any rehabilitative, preventive, or maintenance program, proper exercise prescription can facilitate improvements in musculoskeletal function by addressing the specific needs of an individual. To this end, functional weight-bearing exercises have received a significant amount of attention as the preferred mode of exercise for lower extremity strengthening. 8,10,28 The popularity of weight-bearing

Increased walking knee joint stiffness has been reported in patients with knee osteoarthritis (OA) as a compensatory strategy to improve knee joint stability. However, presence of episodic self-reported knee instability in a large subgroup of patients with knee OA may be a sign of inadequate walking knee joint stiffness. The objective of this work was to evaluate the differences in walking knee joint stiffness in patients with knee OA with and without self-reported instability and examine the relationship between walking knee joint stiffness with quadriceps strength, knee joint laxity, and varus knee malalignment. Overground biomechanical data at a self-selected gait velocity was collected for 35 individuals with knee OA without self-reported instability (stable group) and 17 individuals with knee OA and episodic self-reported instability (unstable group). Knee joint stiffness was calculated during the weight-acceptance phase of gait as the change in the external knee joint moment divided by the change in the knee flexion angle. The unstable group walked with lower knee joint stiffness (p=0.01), mainly due to smaller heel-contact knee flexion angles (p<0.01) and greater knee flexion excursions (p<0.01) compared to their knee stable counterparts. No significant relationships were observed between walking knee joint stiffness and quadriceps strength, knee joint laxity or varus knee malalignment. Reduced walking knee joint stiffness appears to be associated with episodic knee instability and independent of quadriceps muscle weakness, knee joint laxity or varus malalignment. Further investigations of the temporal relationship between self-reported knee joint instability and walking knee joint stiffness are warranted.

Study Design Case report. Objective To highlight the effects of an intervention program consisting of strengthening and neuromuscular reeducation of the gluteus maximus in an elite triathlete with exercise-associated muscle cramping (EAMC). Background Researchers have described 2 theories concerning the etiology of EAMC: (1) muscle fatigue and (2) electrolyte deficit. As such, interventions for EAMC typically consist of stretching/strengthening of the involved muscle and/or supplements to restore electrolyte imbalances. Case Description The patient was a 42-year-old male triathlete with a primary complaint of recurrent cramping of his right hamstring muscle, which prevented him from completing races at his desired pace. Strength testing revealed gluteus maximus muscle weakness bilaterally. Electromyographic (EMG) analysis (surface electrodes, 1560 Hz) revealed that the right hamstrings were being activated excessively during terminal swing and the first half of the stance phase (48.1% maximum voluntary isometric contraction [MVIC]). Outcomes Following the intervention, the patient was able to complete 3 triathlons without hamstring cramping. Strength testing revealed that the right hip extension strength improved from 35.6 to 54.7 kg, and activation of the hamstrings during terminal swing and the first half of the stance phase decreased to 36.4% of MVIC. Discussion A program of gluteus maximus strengthening and neuromuscular training eliminated EAMC of the hamstrings in this patient. Given that the hamstrings and gluteus maximus work as agonists to decelerate the thigh during terminal swing phase and control hip flexion during loading response of running, we postulate that strengthening of the gluteus maximus decreased the relative effort required by the hamstrings, thus reducing EAMC. The results of the EMG evaluation that was performed as part of this case report provides support for this hypothesis. Level of Evidence Therapy, level 4. J Orthop Sports Phys Ther 2010;40(2):112–119. doi:10.2519/jospt.2010.3110

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