Functional recovery after hip replacement: A multivariate cohort study

Osteoarthritis (OA) is the most frequently observed joint disorder in seniors,
and is often an indication for Hip Replacement (HR). In 1997, 112 out of
100.000 inhabitants of the Netherlands underwent HR, leading to a total of
17,400 hip replacements. This number is expected to increase in the coming
years due to aging of the population. Survival rates (that is, time elapsed
until a revision operation) for HR are high, and patients' reports suggest that
patients have less pain and are usually satisfied. Despite these positive
findings, the literature also reports that after one year most HR patients
typically still show a deviant gait pattern, and walk slower than their healthy
peers. Also other Activities of Daily Living, such as walking, stair climbing,
rising from a low chair, entering or leaving a car, or a bathtub, may remain
problematic for quite some time after HR, and patients report feeling
"unstable" in the hip.

More insight into the recovery of function after HR over time, and in the
relationships between function and its potential determinants in patients with
HR, may lead to a better understanding of the problems in patients after HR,
and help identify aims for rehabilitation.
By assessing stability and variability during treadmill walking, and applying
perturbations during gait on a treadmill, we will be able to gain insight into
the stability in patients after HR.

The design is a multivariate cohort study of patients before and after HR, and
a single measurement of healthy controls. At least 35 patients will be measured
before the operation, after one, six, and 12, months. We will register
co-morbidity and peri-operative complications. We will monitor inflammation
mediators, hip abduction/flexion/extension force, hip proprioception in the
frontal and the sagittal plane, oxygen cost of walking, and patient's
self-reports (questionnaires on general health, osteoarthritis-related health,
and fear of movement). All these factors are potential determinants of
functional recovery. To monitor functional recovery itself, a simple ambulant
test for functional ability (the timed stair test) will be administeredand,
self reported measures (SF-36 and WOMAC) will be used, and walking kinematics
will be recorded. In the gait analysis, we will pay special attention to the
coordinative aspects of gait, and the stability during gait.

The major "price" the participant pays is the loss of time: 4 visits to the
VUmc, which, all in all, will each take half a day. Patients are encouraged to
bring relevant others. If they do, both will be offered lunch, drinks, etc.
Participants usually find our research "interesting", and tend to enjoy their
"day off" in our lab. Moreover, they find it comforting that other people
(among whom an orthopaedic surgeon at an academic institution) meet with them,
and examine them.
Technically, the risks are very low. Two researchers (one of which at least a
physical therapist) will be present during all measurement sessions, and during
treadmill sessions, participants are secured in a harness so that falling is
impossible. Therefore, the study does not impose a great risk on injury,
dislocation of the prostheses, or any other medical inconvenience.