EXERCISE IN MOTION POST HIP REPLACEMENT

Exercise in Increasing Range Of Motion Post Hip Replacement

Exercise in Increasing Range Of Motion Post Hip Replacement

Introduction

Stair climbing is a common activity performed by patients with total hip replacements (THRs). A group of 31 clinically well-functioning postoperative THR patients climbed 344 (SD 263) steps during a 12 h period. Despite the fact that it is not an unusual activity, the biomechanics of stair climbing in this particular population have not been well studied. While not the most demanding physical activity possible, stair climbing is arguably more difficult than level walking and places great demands on the fixation stability of both cemented and cementless implants The primary stability of a cementless stem varies between subjects as much as between activities. For example, in a cadaver based in vitro study of cemented implants, cement strains approached failure levels during stair climbing in the proximal portion of the cement mantle. In cementless implants, stair climbing has been shown to generate more micromotion than level walking during in vitro testing.

In addition to the overall resultant hip forces, the out of plane forces and twisting moments (the moment about the long axis of the implant caused by the component of contact force perpendicular to the long axis of the implant times neck length) are particularly important for implant stability and, if high, may lead to implant loosening. Several groups have directly measured in vivo hip forces during stair climbing using telemeterized implants. Most recently, Bergmann et al. showed that in vivo hip forces are 5-10% higher during stair climbing than during level walking in a study of four subjects with instrumented THRs. Moreover, the twisting moments were up to 23% higher during stair climbing than walking at a normal speed.

Unfortunately in vivo data are limited to only a few subjects. Musculoskeletal models can augment the knowledge provided by these in vivo data by providing force estimates in larger numbers of subjects. Accurate hip kinematics and kinetics during stair climbing are necessary for input to such models and can also supplement the force information that the in vivo data can provide by giving a reflection of muscle activity during the activity. Furthermore, it is not known whether subjects with THRs have different stair climbing biomechanics from normal subjects. Differences might occur from muscle weakness, strategies that may have developed before surgery as seen with walking, or as compensation for potential balance deficits demonstrated in some activities.

Andriacchi's group recorded kinematics and external moments of the hip, knee, and ankle during stair climbing in normal subjects. This group found that sagittal plane moments were approximately 1.5 times higher during stair climbing than during level walking. Furthermore, they speculated that this activity would lead to large out of plane forces at the hip because of the large hip flexion angles measured at the instances of the peak moments (Andriacchi et al., 1980). A similar study conducted in a group of normal subjects over the age of 55 years found significantly increased rotational moments during stair ...