The Asian Knee

Bone Mineral Density

Asian populations have been found to have the lowest peak bone mineral density (BMD), the highest being in the Afro-Caribbean population, followed by white populations. BMD in Indian women may be up to 25% to 30% lower than American-European scores.

Vitamin D Deficiency and Rickets

In many Asian countries, vitamin D deficiency has been found to be rampant. Vitamin D deficiency is the cause of rickets in children and osteomalacia and osteoporosis in adults. Genu varum or genu valgum has been described as the most common deformity in patients with rickets. Varus knee is the main manifestation of osteomalacia.

One study has reported that a 4% to 6% increase in varus alignment increased the loading in the medial compartment by up to 20%. Such increased stress on the articular cartilage could lead to degenerative changes. One other study found malalignment to be a risk factor for development of OA. Varus deformity as a causative factor for OA needs to be evaluated further. However, a systematic review has shown that after OA has set in, a malaligned knee joint is more susceptible to progression of the OA.

We recommend obtaining vitamin D blood levels in all Asian patients and treating any deficiency preoperatively. In our patients we have noted vitamin D–deficient patients showing poor Western Ontario and McMaster Universities (WOMAC) scores.

Kneeling

Kneeling probably is the most common floor-based activity performed across the world. There are various forms of kneeling. White populations kneel with lesser hip and knee flexion compared with kneeling in seiza —a Japanese formal sitting position—or Namaz —a Muslim prayer position (see Fig. 25.2A to C and Table 25.1 ). These different forms of kneeling involve differences in the position of the ankle and torso.

Kinematic studies in knees of white populations have shown that with increasing flexion, there is posterior roll-back of the femoral contact point on the tibia and the lateral condyle excursion is far greater than medial condyle, so much so that in the final phase of deep flexion the lateral condyle slides off posteriorly from its contact on the tibial condyle. There is also a subtle but definite and important difference in this movement between white and Japanese populations. In the Japanese the lateral condyle was found to have similar excursion as in the white population study, but the medial condyle remained much more stable with little excursion. Other biomechanical studies have shown that repetitive kneeling can damage the cartilage and menisci in the natural knee, and the increased tibiofemoral contact pressures can lead to polyethylene wear in the implanted knee.

Kneeling kinematics after TKA have been studied to follow normal knee kinematics, although it was observed that knee flexion angles were smaller and patella showed sagittal plane tilting.

Cross-Legged Sitting

Cross-legged sitting, also known as the tailor or lotus posture ( Fig. 25.1D ), involves a complex combination of movements of the hip, knee, and ankle joints. At the hip there is flexion (80 to 101 degrees), abduction (30 to 57 degrees), and external rotation (36 to 52 degrees); at the knee joint there is flexion (130 to 142 degrees) and internal rotation (17 to 34 degrees), and at the ankle there is minimal planter flexion assumed for this posture.

Cross-legged posture in Eastern culture is most frequently assumed while sitting on the floor, which means that it also entails getting into the posture from standing position and rising back into the standing position from the floor. Alternatively, this posture can be assumed on a higher surface, such as a bed or platform, which does not demand the additional maneuver of having to descend and ascend to or from the floor.

Squatting

Squatting is a resting postural complex that involves hyperflexion at the hip and knee joints, and hyperdorsiflexion at the ankle and subtalar joints (see Fig. 25.2E and Table 25.1 ). Squatting is an age-old posture assumed commonly for toilet facilities in India and other Asian countries. Even after knee OA sets in, squatting continues to be undertaken, especially in rural areas, out of necessity to use the toilet facility. A modified semi- or half-squat position may sometimes be adopted as a compromise. Squatting and partial squatting is also commonly performed as part of yoga, dance, and exercise. Apprehension exists in allowing this activity post-TKA for fear of increased stress on the polyethylene and implant fixation, which could affect the long-term survival. A study by Nakamura et al. concluded that deep flexion did not affect the long-term durability of one high-flex ceramic implant. In addition, a report by Mizu-Uchi concluded that squatting exerts forces 2.2 to 2.3 times the body weight, which is actually equivalent to that in walking. Similarly Thambyah found that tibiofemoral contact force in squatting was not much different than in walking. Indeed the ground reaction force was reported to be higher in walking than in squatting. On the other hand, they found that the tibiofemoral shear force, which is directed posteriorly in normal walking, becomes directed anteriorly in squatting. It was also observed that the descent and ascent from a squatting position lead to higher contact forces. These factors would have bearing on the stresses and fixation of tibial implant when squatting is undertaken after TKA.