As Dr.Stan has opted out ill help you here in answering all your questions,
First of all im sorry to hear about your father and i hope i will be able to help with my answers
1) what is avascular necrosis and how does that relate to these facts? Is it caused by the 11 day delay in surgical intervention?
Avascular necrosis is basically the death of the head of the thigh bone (femur) due to loss of blood supply to that area. this occurs because the head of the femur is highly vascular and needs constant blood supply to stay healthy. in case of frature of this area the blood supply is cut off and the bone starts to die. This condition is a surgical emergency in the sense that if timely intervention is nor made the head of the femur dies and leads to several problems later on. Now the delay in your fathers diagnosis definitely caused the bone to die, maybe if he had been doagnosed earlier then he could have avoided the total hip replacement and gone for some other modality but regardless at such an age the therapy most surgeons opt for is THR. but maybe the other complications could have been avoided.
2) Could this 11 day delay be the cause of his inability to walk now? I've heard that a delay in time to reduction can impair chances of successful recovery.
As i have already mentioned this can cause the delay in healing process specially at an age that your father is. This can cause delay in healing after surgery, increased rate of infections etc.
3) How does a contracture and neuropathy develop after surgery?
A contracture is basically hardening of the muscles which occurs due to fibrosis of the tendons and the muscle. the fibrous tissue is basically a type of tissue that is stronger and less elastic than other types of tissues and once this muscle forms then it is difficult to break down or in the region where it is formed that region is difficult to move. this occurs due to less movement or rather decreased activity of the area after a stroke or an injury for that matter. in your fathers case it proabably occured because he had a stroke previously and the THR combined with that stroke impaired his ability to properly uindergo physical therapy. The pain from the surgery plus the previous stroke both combined in such a way that he could not exercise his muscles, leading to the formation of contractures.
Now the neuropathy can have developed due to several regions, it could have occured due to damage to the nerve during surgery, sometimes during surgery the sciatic nerve can be nicked or damage and once it heals it leads to improper relay of signals which causes neuropathy. Another cause be the contracture itself which can have caused the nerve to become entrapped at some location in the leg leading to the development of the neuropathy.
4) in this case, is it foreseeable that a total right hip replacement could result in this sad outcome?
Well this is a very difficult question to answer, because your fathers case is not a simple case. now the stroke combined with the THr definitely has impaired his ability to ambulate properly but there was no way of knowing this before the surgery. unfortunately everything that could go wrong has gone wrong in your fathers case. there is always the risk of complications like this of occuring in a THR and they did in your fathers case. In THR contractures can form alongwith infections due to inability of the patient to undergo proper rehabilitation as was the case with your father.
Right now the best thing you can do is get a Nerve Conduction Study to determine the cause of the neuropathy and if its entrapement then this can be relieved by releasing the nerve from where it is entrapped. the second thing which can improve your fathers symptoms is that of physical therapy alongwith Devices known as continuous passive motion machines which
are very popular, especially following surgery of joints. Continuous passive motion machines (CPM) are specifically adjusted to each individual's need. The joint is mechanically moved through the patient's tolerable motion. CPM machines have been proved to accelerate the return motion process, allowing patients more function in less time.
Another option is Casting or splinting
which are techniques are used to provide a constant stretch to the soft tissues surrounding a joint. It is most effective when used to increase motion of a joint from prolonged immobilization. It is also popular for treating contractures resulting from an increase in muscle tone from nerve injury. After an initial holding cast is applied for seven to 10 days, a series of positional casts are applied at weekly intervals. Before the application of each new cast, the joint is moved as much as can be tolerated by the patient, and measured by a goniometer. When as much motion as possible is obtained after stretching, another final cast is applied to maintain the newly acquired motion.
Lastly surgery can be done to release the contracture as well.
i hope this answers all your questions
If I have been helpful,
BONUSES and POSITIVE FEEDBACK is always appreciated
Please feel free to ask me follow up questions, also note that this is NOT a substitute for a visit to the doctor.