Mobility after proximal femoral fracture: the relevance of leg extensor power, postural sway and other factors

Age and Ageing, July, 1995 by S.E. Lamb, R.E. Morse, J. Grimley Evans

Introduction

Recent studies have demonstrated that at 1 year after proximal femoral fracture (PFF), only 40% of survivors who had been ambulant without a walking-aid prior to the fracture returned to that state. For many, walking was more severely compromised [1, 2]. Mobility is essential to independence [3], yet we have little understanding of the cause of its impairment after PFF.

Aniannson et al. [4] reported that, compared with age-matched controls, women who had sustained a PFF demonstrated an accelerated reduction in fast twitch muscle fibre size in the quadriceps. These fibres are important in generating explosive leg extensor power (LEP) [5]. Bassey et al. [6] have demonstrated that LEP is essential to mobility in elderly subjects who have chronic conditions. 'Thresholds' or minimum amounts of LEP could be identified below which mobility became impossible [6]. The effect of PFF on LEP has not been studied, but the injury, surgery and hospitalization are likely to be detrimental.

Balance is also likely to be an important factor. Postural sway is widely used as an inverse index of balance [7]. Previous studies have reported postural sway in 50-64-year-old subjects, 6-30 months after fracture, to be greater than in age- and sex-matched controls. Sway was correlated with mobility [8].

Factors such as poor pre-injury mobility, fracture type, and advanced age have been associated with poor outcome after PFF [9, 10]. However, it is unclear to what extent these factors govern recovery. The aim of this study was to identify significant factors in the early stages of recovery of mobility after surgical fixation of PFF in previously healthy elderly women over the age of 75 years.

Subjects

Women aged 76-96 years were recruited 1 week after surgical fixation of PFF. Subjects were excluded if they had acute physical or mental illness or distress, scored less than 7/10 on a mental, test score [11], had respiratory dysfunction, uncontrolled cardiac failure, blood pressure over 200 mmHg systolic or 100 mmHg diastolic, a pathological fracture, neurological impairment, or surgical complications. Patients taking drugs likely to affect neuromuscular function were excluded. Other drug regimens were not exclusion criteria, nor were chronic non-limiting age-associated conditions, such as osteoarthritis. Subjects were medically assessed for eligibility for the study protocol, which had ethical committee approval. Forty women agreed to take part in the study after it had been described to them.

Methods

Pre-injury functional ability and mobility were assessed using the Barthel Index [12] and a self-report of pre-injury mobility [13] (Table 1). Subjects were asked to rate their pain levels for the 24-h period prior to the study, using the method described by Keene et al. [1] (Table I). LEP was measured using a Nottingham leg extensor power rig [14]. The patient was seated, and the rig adjusted to accommodate each leg. The subject was instructed to push the leg into extension with maximal effort. Strong verbal encouragement was given and a maximum of 10 tests were performed. The output was a product of the force and the rate of force generation during a single leg extension [14]. Maximal power output was recorded for the fractured leg (LEPf), uninjured leg (LEPg), and summed to give LEP in both legs (LEPb). The difference between legs (LEP diff) was calculated by subtracting LEPf from LEPg. Readings were in watts (W), normalized by body weight (W/kg). Postural sway was measured using an ataxiameter (Technical Forum, Nottingham), which gives a 1-min cumulative reading of sway (in cm) from the vertical when standing. The subjects stood with their feet together and eyes open. Sway measurements were taken at the level of the 2nd lumbar spinous process. Walking ability was assessed over two distances, 10 ft and 50 ft selected to represent the minimal and maximal requirements for indoor mobility (1 foot = 0. 305 m). Subjects were asked to walk 1 0 ft from a stationary position at their comfortable walking speed, with a walking-aid and assistance of a therapist if needed. They did this twice and the faster speed was recorded. On the second test subjects were encouraged to extend the walk to complete the 50-ft course. Ability to complete the distances, the use of walking-aid and the time taken were recorded. The ability to climb stairs was assessed on a staircase of five steps (each of 15 cm), with handrails on both sides. Ability to complete the task, timed from the footfall on the first step to footfall on the top step, the use of support (one or two rails) and climbing pattern (one step at a time, or reciprocating gait) were recorded.

Table I. Self-report of pre-injury mobility and pain Before your fall were you able to: 1. Maintain your balance whilst sitting in a chair? 2. Stand up from your chair? 3. Walk inside your home? 4. Walk outside your home? 5. Walk outside quickly e.g. when crossing a road? 6. Bend down to pick something up off the floor? 7. Climb a flight of 12 steps?