An appraisal of rehabilitation regimes used for improving functional outcome after total hip replacement surgery

This study aimed to systematically review the literature with regards to studies of rehabilitation programmes that have tried to improve function after total hip replacement (THR) surgery. 15 randomised controlled trials were identified of which 11 were centre-based, 2 were home based and 2 were trials comparing home and centre based interventions. The use of a progressive resistance training (PRT) programme led to significant improvement in muscle strength and function if the intervention was carried out early (< 1 month following surgery) in a centre (6/11 centre-based studies used PRT), or late (> 1 month following surgery) in a home based setting (2/2 home based studies used PRT). In direct comparison, there was no difference in functional measures between home and centre based programmes (2 studies), with PRT not included in the regimes prescribed. A limitation of the majority of these intervention studies was the short period of follow up. Centre based program delivery is expensive as high costs are associated with supervision, facility provision, and transport of patients. Early interventions are important to counteract the deficit in muscle strength in the affected limb, as well as persistent atrophy that exists around the affected hip at 2 years post-operatively. Studies of early home-based regimes featuring PRT with long term follow up are needed to address the problems currently associated with rehabilitation following THR.


Background
Symptomatic hip osteoarthritis occurs in 3% of the elderly [1] and is associated with poor general health status [2]. Treatment strategies for hip pain have usually involved conservative measures (analgesia, exercise, education, weight reduction), with surgical intervention (total hip replacement; THR) being the most effective treatment for end stage disease [3]. The National Joint Registry for England and Wales reports that the number of primary total hip replacements performed in England and Wales in 2009/2010 totaled 79413, which is a steady rise from the numbers reported in 2008/2009 (77608) and 2006/2007 (51981) [4].
The most common preoperative complaints by patients who elect to have THR are pain and loss of mobility [1,5]. It therefore follows that the most commonly reported outcomes of THR in the literature relate to pain relief and restoration of mobility [1]. It is clear that a major predictor of outcome after THR is the preoperative status -worse preoperative status is followed by a poorer absolute outcome as defined by several outcome measures [6]. Outcome studies of pain reduction and range of motion restoration, usually conducted 3 to 6 months after THR, indicate an overall satisfaction by patients and physicians [7]. However, outcome studies performed at least 1 year after THR reveal that limitations in physical function remain even in the absence of pain. These persisting impairments include decrements of 10-21% in muscle strength and postural stability of the involved hip relative to the non-operated hip at 1 year post-THR surgery [8,9], with these deficits still evident 2 years after surgery [2,10]. Interestingly, Long et al. [10] reported that muscle weakness during stance, along with deterioration of the Harris Hip score, were the most consistent findings in patients who developed loosening of the hip components; implying that muscle weakness may result in reduced protection of the prosthetic implant fixation.
Prior to surgery, there is a general deficit in muscular strength along the affected limb as compared to the contra-lateral (healthy) side in patients with unilateral hip osteoarthritis (OA) [11], and muscles such as the abductors, vastii, rectus femoris and psoas show marked atrophy. This is evidenced by reduced cross sectional area and an infiltration of non-contractile components; i.e. an average 10% increase in fatty infiltration of muscle (myosteatosis) in the affected limb compared to the healthy one [11]. As well as reducing muscle strength, myosteatosis also exacerbates fall risk [12]. This muscular dysfunction is likely to contribute to the reduced ambulatory capacity of OA patients, as loss of lowerlimb muscle strength has been shown to predict the onset of activities of daily living dependence in the elderly [13]. Consistent with the persisting functional deficits following surgery, these atrophic changes about the hip are still evident up to 2 years following THR surgery [11]. Frail elderly persons with sarcopenia often undergo musculoskeletal-related surgery such as THR, and the hospitalisation-associated immobilisation further compromises the skeletal system, with potentially grave consequences [14]. Earlier operation may prevent the development of persistent atrophic changes that occur after THR and there is a suggestion by Rasch et al. [11] that fatty infiltration may be reversed by intensive rehabilitation [11].
There have been considerable technical efforts towards optimising surgical treatment of patients with arthritis of the hip, for example with over 100 varieties of hip prostheses being available, multiple types of bearing couples and several surgical approaches. As technology and surgical techniques for total hip replacement (THR) improve, patient expectations, including for an early return to normal physical function and activities, have also increased [15]. However, the actual health gain for many of these innovations relative to "standard" THR is small in terms of patient function and quality of life [16].
In the past, a prolonged hospital stay after THR surgery incorporated a period of supervised rehabilitation to try to achieve restoration of physical function. However, due to the introduction of initiatives such as integrated care pathways and considerations of cost and increasing patient satisfaction, the length of hospital stay following joint replacement has been substantially reduced [17]. Mean length of stay after THR over the past decade has declined from 3 weeks to 4 days [18]. Rehabilitation is therefore increasingly important following total hip replacement. The aim of this review is to systematically investigate the literature with regards to the highest-level evidence (randomised controlled trials) for studies of rehabilitation programmes that have tried to improve function after this common surgical intervention.

Methods
Studies were eligible for the review if they met the following criteria: 1) randomised controlled trial of exercise rehabilitation interventions to improve functional outcome in the post-operative period; 2) target population includes patients undergoing total hip arthroplasty for osteoarthritis; and 3) publication in English language. For the purpose of this review, early interventions occurred ≤1 month after surgery and late interventions were ≥ 1 month after surgery. This distinction is important as it has been noted that muscle strength declines 4% per day during the first week of immobilisation after major surgery, making it important that rehabilitation is commenced as soon as possible afterwards [19].
Studies were identified from computerized search of MEDLINE (1950 to date), EMBASE (1980 to date), and CINAHL databases. A set was created using the terms: 'total hip arthroplasty AND replacement' and yielded 6559 articles. A search strategy was then built by adding the terms 'exercise', 'rehabilitation', 'physiotherapy', 'functional outcome' to 'total hip arthroplasty AND replacement'. Restriction of the articles obtained from the computerised search to randomised controlled trials and ensuring that the intervention was timed in the post-operative period led to the identification of 15 appropriate studies ( Table 1). The studies identified were assessed using the following parameters: 1) whether they were home or centre based, 2) the follow up period used for functional assessment, 3) the interval from surgery to the rehabilitation intervention, 4) the exercise intervention carried out, 5) the outcome measures utilised, and 6) any evidence of dislocation as a complication. For the last parameter listed (dislocation), contact by email was made with the author of any study in which the rate of dislocation was not documented in the article.

Results
From Table 1, it can be seen that 11 interventions were performed in a rehabilitation centre, 2 involved a direct comparison between home and centre based interventions and 2 trials were home based. The data shows that, if early intervention is defined as commencing within a month of surgery, such an intervention is more likely to have a beneficial effect if it is performed in a centre and involves progressive resistance training (PRT; i.e. strength training wherein the resistance (weight) lifted is increased in accordance with improved strength     to ensure maintenance of a constant relative intensity) ( Table 2; 6 out of 6 centre based studies [14,21,23,24,26,27] involving resistance training proved beneficial). The only centre based intervention, by Gremeaux et al., [22], that led to significant improvements in muscle strength without progressive resistance training utilised electrical stimulation. This has been shown by Suetta et al. [14] to not be as efficacious when directly compared to PRT (Table 1). Both home based intervention studies identified in this review [5,25] were carried out in the late phase (> 1 month post-operatively) and led to significant improvements in functional outcome parameters after short periods of follow up (8 and 12 weeks respectively). The other 6 studies reviewed include 2 comparing home and centre based interventions [20,28] and 4 others performed in the early phase in a centre setting [29][30][31][32] but without the use of progressive training. Their limitations and findings are as detailed in Table 1.
The follow up periods for the centre based studies varied from 7 days to 24 months (Table 1). In terms of the follow up periods that were longer than the interventions used, Liebs et al. [27] show with their ergometer study that the benefits of a resistance program are sustained for 24 months from surgery which helps to address the functional deficits identified after THR. Mahomed et al. [28] demonstrated that there is not much difference at 1 year between home and centre based post-THR standard physiotherapy interventions in terms of subjective functional outcome (measured with the WOMAC), but there was no progressive training included in the prescribed programs used and this may explain the lack of a significant difference between the groups.

Discussion
'Standard physiotherapy', (i.e. not involving resistance training) following major surgery enables most patients to regain basal levels of function but leaves them with significant muscle wasting as it lacks the intensity of exercise required to elicit muscle hypertrophy [14,33]. The most commonly used rehabilitation regimes for elderly individuals are based on functional types of exercises without external loading. However, this type of intervention not only fails to elicit increases in muscle mass but does not prevent further muscle atrophy [34].
In contrast, high-intensity PRT is an extremely effective and safe method for inducing muscle hypertrophy and increasing muscle strength and subsequently improving functional performance in healthy individuals, those with chronic disease e.g. rheumatoid arthritis [33], and the elderly [35][36][37]. An unpublished survey from our institution of physiotherapy practice around the UK after THR revealed that 73% of qualified physiotherapists knew what progressive resistance training entailed but only 32% used it in their prescribed programmes after THR. PRT typically elicits positive health and performance adaptations by challenging the skeletal muscles with loads that can be lifted repetitively for 8-15 repetitions maximum (RM) per set before the onset of neuromuscular fatigue i.e. the point at which appropriate technique can no longer be maintained [3,38]. PRT sessions are optimal when followed by periods of recovery ranging from 48 to 72 h to allow for physiological super compensation (i.e. positive adaptation) [39]. To facilitate continued adaptation and avoid the onset of a plateau in physiological adaptation, training intensity (i.e. load) and/or training volume (i.e. the total number of lifts) are progressively increased in line with training response [39]. Health and performance are maintained with continued training [40] and PRT is well established as a safe and beneficial exercise modality for individuals of all ages and fitness levels, including those afflicted with severe chronic illnesses [33,39,41]. Additionally, PRT is particularly beneficial for elderly individuals given its efficacy in counteracting sarcopenia, reducing fat mass, abating osteoporosis, and reversing the many physiological and functional impairments that accrue with age [4-6]. The positive benefits of this method of rehabilitation are evident with the 5 randomised controlled trials identified in this review (Table 2).
A major disadvantage of programs used in the postoperative period following THR is the need for patients to exercise under the supervision of professional staff at a hospital or rehabilitation centre [20]. This makes program delivery expensive due to the high costs associated with supervision and transport. In addition, some THR patients are excluded because of difficulties with mobility [7]. A similar exercise regime that could be performed at home would overcome these cost and logistic implications.
A limitation of the home-based interventions is that follow-up did not extend beyond the end of the exercise interventions periods. Thus, it is not clear whether the benefits evident at the end of the exercise intervention are maintained in the longer term. The other obvious shortcoming is the lateness of the intervention in the home setting and consequently the failure to ameliorate or prevent the exacerbated loss of muscle and function after surgery. A recent systematic review by Di Monaco et al. [42] suggests that the difficulties in THR rehabilitation research are that there is a lack of multicentre clinical trials with large sample sizes to inform the design of optimal physical exercise programs.
It follows that with the adverse impact of major surgery on muscle mass and therefore strength and function, being able to provide an intervention in the early post-operative period is essential. The intervention should also obviate the problems of cost and transport that supervised, centre-based rehabilitation programs necessarily involve. Providing patients with the impetus to rehabilitate themselves with minimal supervision in their home environments may be the answer.
A major concern with orthopaedic surgeons is dislocation of the hip arthroplasty (incidence after primary THR of 1-9.5% [43] on patient mobilisation and the instructions patients have to adhere to afterwards take this into account. These include a restriction of hip flexion to less than 90°, no crossing of the legs, and elevation of toilet seats and chairs in the house etc. From this systematic review of 15 randomised controlled trials, the dislocation rate in the pooled sample of patients who underwent the interventions described was 0.77% (4 recorded dislocations in a pooled sample of n = 516) whilst the rate in patients who were in the normal control groups was 1% (5 recorded dislocations in a pooled sample of n = 505). Thus, it is safe to conclude that these exercise programmes are not associated with an increased risk of dislocation.

Conclusions
Total hip replacement surgery provides good relief for patients' pain but fails to fully restore physical function. This systematic review demonstrates that significant improvements in muscle strength and function are achievable with PRT. Regardless of the timing of the intervention, PRT appears to have a significant benefit on patient function following THR. Late PRT interventions do work and are safe, and they have been performed mainly in the home setting but the studies done have short periods of follow up and have a further limitation of the pre-existing functional deficit due to the timing post-operatively. Early PRT regimes identified in the studies reviewed in this article have shown the need for a centre-based approach and this has demonstrable benefit but there are issues of high costs of transport and supervision. Early home based PRT studies that are effective and safe; with adequate follow-up after THR surgery would potentially address these issues.