Total hip and knee replacement is one of the more common elective surgeries being offered both by the public and private sectors in the UK and US. Since the 1960s, when the first hip replacement surgery was performed, there have been many technological advances in implant design and operating procedures. Unfortunately, post-acute care has remained largely unchanged, and today, around 20% gain no functional improvement. This article explores what could be on the horizon to improve overall patient outcomes.
Perioperative Planning
To plan an effective post-operative care pathway, it is important to understand how Osteoarthritis (OA) at the hip or knee joint affects a patient, since it was given as the main reason for undergoing total joint replacement surgery in 98% of knee patients and 91% of hip patients. Cartilage damage causes bone on bone contact at a small area within the joint which exposes nerves. The result is extreme pain at the joint, particularly when walking. This may cause the patient to become more sedentary, and adapt their gait to minimise pain. These gait kinematic adaptations are well documented for both hip and knee OA. As the patient often waits at least a year in the UK, by the time of the operation the muscles in the lower limbs will have adapted accordingly and many will have weakened.
Patients undertake joint replacement surgery to reduce or remove joint pain and improve joint function, so they can return to their normal activities. As the median age for joint replacement is 70, these activities will almost certainly include walking and may include running, cycling, swimming and racket sports.
Surgery
Joint replacement procedures are recorded in a National Joint Registry and reported annually in the USA and UK.
The data on the implant design and procedure is comprehensive, providing a full audit trail for surgeon and implant designers. Surgical revision rates provide a good measure of implant performance and drive the evolution of implant designs. New surgical techniques, such as the use of a robot and coronal plane alignment of the knee are also now being adopted.
Post-operative care
The UK and USA have both adopted the Enhanced Recovery After Surgery programme for joint replacement patients, and joint mobilisation within 24 hours is the aim for every patient.
Patients are discharged from hospital once mobilised, unless there are complications. A hospital physiotherapist or occupational therapist should give advice on self-directed rehabilitation to follow at home. But then, the system is completely blind to how well the patient is recovering.
Follow-Up
Performance Related Outcome Measures (PROMs) capture the benefit of the surgery to the patient, using the Oxford Hip Score (OHS) or Oxford Knee Score (OKS), as appropriate. These questionnaires are collected in the UK and US at 6 or 12 months post-operative, respectively. The OHS and OKS comprise twelve questions, six of which relate to pain and six relate to the ability to perform certain activities. It is well known that pain scores and a person’s perception of their ability to perform a task are notoriously subjective and no objective data is captured to ascertain the patient’s ability to move.
In both countries only between 30 and 40% of patients return their post op forms. There clearly is no incentive to do so, which means important information is lost.
Drawing conclusions from this low response rate is susceptible to a large error.
What Is Missing in Postoperative Care
Technological advances in implant design and operating procedures have been significant over the last two decades. Yet we still rely on patients to rehabilitate at home with minimal technology to monitor or guide them. This is one of the few areas of medicine where the result of a high cost intervention is not supported with high quality objective data.
As discussed, gait kinematics change significantly in people with OA of the hip or knee. The brain has learnt to walk a particular way to minimise pain and whilst the OA joint is most affected, muscle loss is not limited to this joint.
When the joint pain is removed following surgery, there is nothing to retrain the brain to walk properly again. So many people remain with their gait deficiency but without pain. Does this matter? The answer is yes for many reasons.
Walking is a cyclic motion with motion of the lower limbs in the direction of travel. The upper body remains nominally still and the cyclic movement is from the hip and knee joints.
Below is an example of a total knee replacement patient at 6 weeks post-surgery, with the range of motion at the hip and knee joints and the pelvis, thigh and calf segments. Traffic light coding is used to identify how far the range is from normal. It is clear that the right knee is not functioning correctly, with the knee bend during the swing phase at only 39⁰. Knee bend ensures the foot clears the ground as it moves under the body, so this patient is at risk of tripping. The hip range is also reduced on both sides, reducing the stride length, and the stride time has increased. This patient had a resulting gait speed of 0.79 m/s.
With this knowledge a patient can be provided with a personalised exercise plan. After just 12 weeks of the exercise plan, this patient was walking better, as shown in the diagram, with a knee range of 47⁰ and a healthy gait speed of 1.2 m/s.
This patient was lucky enough to receive a guided recovery plan, but studies on both hip and knee replacement patients show that only around 50% recover a normal gait. The others are at an ever-increasing risk of a fall, constituting a fresh burden on the health service, and the effect on the patient can be permanently debilitating.
In summary, we have highly effective procedures for hip and knee replacements, but almost no science backing the post-operative care. All the measurements are subjective, and over 60% of patients don’t even respond. No other medical procedure relies purely on subjective input; isn’t it time we bring technology in to post- acute care for total joint replacement?