Nerve injuries after total hip replacement

By Mr NIKHIL SHAH, consultant trauma and orthopaedic surgeon at Wrightington Hospital.

Total hip replacements are very successful operations and have been shown to provide good pain relief from hip arthritis; however, like other successful surgeries they can be associated with some risks and complications. This brief write-up discusses some of the common nerve problems and the reasons why they might happen.

[ONE OF THE complications that can happen is injury to the nerves around the hip during surgery. Not only can that cause clinical problems for the patient, such as neuropathic pain, loss of power and muscle weakness or loss of feeling, but it can also be a source of allegations of negligence in performing the surgery against the treating surgeon.

The actual incidence of nerve injuries after primary total hip replacement is low and is generally stated to be around 1% or less in most studies. There are two important nerves around the hip that commonly figure in nerve injury related issues. They are the sciatic nerve and the femoral nerve.

The sciatic nerve is located towards the back of the hip (posterior) and the femoral nerve on the front of the hip (anterior). The role of the sciatic nerve is to provide sensory and motor function to the leg and foot. The peroneal division of the sciatic nerve is important in enabling the patient to ‘dorsiflex’ the ankle and toes – that is, move the ankle and toes backwards towards the head – and is the more commonly injured component. When that is injured, the patient may develop a ‘foot drop’: in other words, the patient cannot extend or dorsiflex the ankle and toes. There can also be loss of feeling in and around the foot and sometimes quite severe nerve pain.

The femoral nerve, on the other hand, supplies the quadriceps muscle and injury to that nerve can lead to muscle weakness in extending or straightening the knee. Both can lead to problems in gait.

There are certain patient-related factors which increase their vulnerability to nerve injury. They include high BMI (obesity), female gender, previous hip surgery, presence of previous metalwork around the surgical area and certain hip conditions such as total hip replacement for hip dysplasia. The surgical approach may occasionally determine which nerve is more at risk.

It is vital that the risk is discussed with the patient before surgery during the counselling and consenting process, to ensure that the patient is well educated and makes an informed decision.

Iatrogenic injury can occur to the nerve due to retraction from surgical instruments, direct injury from a knife, drill or saw, thermal injury from the diathermy or cement polymerisation or pressure-related ischaemia of the nerve. Other causes also include inadvertent lengthening of the operated leg beyond the tolerances of a particular nerve. Post-operative nerve problems can occur due to compression from a haematoma. However, the commonest reason for nerve injury still appears to be ‘idiopathic’ – or unknown.

It is important to appreciate the causes of nerve injury and take all precautions in performing the surgery to protect the nerve. Some surgeons prefer to feel the nerve and know where its position is, while others visualise the nerve to see where it is lying. Utmost care must be exerted to protect the nerve throughout the surgery, especially when using retraction or sharp instruments in close proximity. There are welldescribed surgical techniques to protect the nerve that surgeons are familiar with.

Unfortunately, however, nerve injuries can occur even when the surgeon takes all the necessary precautions to avoid the problem. Sustaining a nerve injury during total hip replacement is not synonymous with negligence. It is recognised that it can also be a non-negligent complication that may occur even when the surgeon has taken all preventive measures to avoid an injury.

It is important after surgery to check for nerve function as soon as the patient’s anaesthesia wears off. The surgeon needs to be familiar with common treatable causes of nerve injury such as compression from a haematoma, which may in some cases need repeat surgery. It may be necessary to obtain certain tests after surgery to check if a treatable cause can be identified. An early second opinion from a colleague is usually very helpful.

Special imaging scans may be needed. An opinion may also be obtained from a specialist nerve surgeon, either locally or regionally, to obtain advice about further management which may include reexploration and sometimes repair of the nerve. It can be a distressing time for the patient and it is important to be open and honest to the patient if a complication has occurred. A pain management specialist may need to be involved to help with the neuropathic pain. A foot drop is usually managed with a foot drop splint and physiotherapy to avoid muscle tendon contractures. Nerve conduction studies and electro-myography may be quite helpful in determining the type of injury and the prognosis. The prognosis for recovery depends upon whether the injury is incomplete or complete. Incomplete injuries may slowly demonstrate a reasonably good or sometimes a complete return to function; but that often takes 1-2 years before the recovery is complete or even longer in some cases. q www.yourexpertwitness.co.uk 41 41