The Hip joint can be approached in many ways and therefore many different exposures have been described. The choice of which approach to use depend on the type of surgery, what part of the hip needs to be exposed, age of the patient and surgeon’s preference and expertise.
When approaching the hip it is also important to consider whether the surgery is done for trauma or elective surgery, whether the patient is an adult or a child whether it is conservative hip surgery or replacement surgery and what part needs to be accessed for the specific surgery such as the acetabulum, femoral head or whether both need equal access as in total hip arthroplasty.
The main aim of this chapter is to discuss the available surgical approaches in the adult hip when elective reconstructive surgery is done such as total hip resurfacing and revision hip arthroplasty.
The advantages and dis-advantages and the clinical relevance of these approaches to each surgery and basic surgical steps are discussed including the traditional approach and the modification of these approaches.
For completion of the chapter most approaches and classifications are mentioned but the emphasis is mainly on the common approaches used in hip arthroplasty. A good approach to the hip should have good access to both femoral head and acetabulum, should have minimal dissection of soft tissues, leading to reduced operative time and blood loss, less post operative pain and early mobilisation, least risk of damage to neurovascular bundles muscles and tendons with minimal risk of infection thrombosis and dislocation. However in practice there is no one ideal approach hence many approaches have been described and used among orthopaedic surgeons over the years.
2. Classification of different surgical approaches
Surgical approaches to the hip joint can be classified in many ways. One simple classification is based on the direction of approach. (Fig 1) The common approaches used based on this classification are the anterior, antero-lateral and posterior. Some of the different ways of classifying surgical approaches to the hip is given below. 
Based on the direction
Lateral and antero lateral type
Combined e.g. anterior and posterior
Based on incision and invasiveness
Standard incision e.g. Posterior
Mini incision posterior (MIS)
Based on type od surgery
Open surgical e.g. anterior
It is also important to know that certain new approaches described are essentially a modification of an existing approach. E.g. Trochanteric flip approach is a modification of an anterior type approach. 
3. Surgical approaches to the hip joint
Before performing any surgical approach it is important understand the anatomical principles that lie behind the surgical dissection.
Like in all orthopaedic surgeries positioning the patient, draping and preparing the area, identification of landmarks and making the incision along skin creases, are important to remember. It is also important to note that all incisions should be made along the identified line of incision but the initial incision is best made within the middle half of the incision line so that if needed this can be extended in either direction. Previous concept of “Big surgeons make big incisions” does not hold true in modern day practice as the demand is for mini incisions and key hole surgery as they give a better cosmetic outcome.
Another principle in operative orthopaedic surgery is the attempt to go directly to the operative area whether it is a bone or a joint. This minimises the lateral dissection thus avoiding damage to soft tissues such as nerves and vessels.
The concept of “internervous plane” is important to understand before any surgical approach is done. This means that all deep dissection should be done by dissecting and separating the muscles between two nervous planes so that all muscles supplied by one nerve and it’s branches are retracted towards one side to avoid damage and denervating the muscles. (Fig 2)
It is not always possible to dissect along the internervous plane. Sometimes dissection planes are developed by splitting the muscles. (Fig 3) The principles of muscle splitting incision are
Always muscles are split longitudinally along the line of the fibres.
Splitting is done away from the neuromuscular junction to avoid denervation.
Bulk of the muscle is retracted along with the nerve-so that most of the muscle will retain the nerve supply.
In the next few paragraphs the following approaches are described in relation to the clinical implications.
Anterior type approach is Smith Peterson approach
Mini incision anterior approach
Direct Lateral /Hardinge
Antero-Lateral /Watson Jones
Southern Approach 
Postero-medial (Ferguson Approach)
Modified and combined approaches
Trochanteric Flip Ganz 
Antero –lateral minimally invasive 
Mini incision posterior approach 
Modified antero-lateral 
Combined approaches 
Out of these approaches it is important understand that the medial approaches are rarely used in hip arthroplasty due to poor access to acetabulum and femoral head.
Even though a detailed description of each surgical approach is beyond the scope of this chapter all the salient features of above approaches are discussed with regard to their key steps, key advantages, key limitations, specific complications, common surgical procedures done through the approach, modifications of the traditional approach and other key issues.
The approaches described in depth below are the surgical approaches used commonly in hip arthroplasty.
4. The anterior approach (Smith-Petersen)
This approach initially described by Smith-Peterson  is one of the approaches but not a very popular approach used by arthroplasty surgeons as the femoral exposure is limited. It is mainly used for arthrotomies to drain the hip in presence of infection. The key steps and the details are given below.
Position: Supine with a pillow under the pelvis on the operating side
Incision: Longitudinal incision lies between anterior iliac crest towards upper thigh curving over anterior superior iliac spine.
Soft tissue dissection: This is between sartorius and the tensor fasciae lata and rectus femoris and gluteus medius.
Internervous plane: Lies between the sartorius (Femoral nerve) and the tensor fasciae latae (Superior gluteal nerve)
Arthrotomy: Adduct and externally rotate the leg and incise the capsule longitudinally or with W or T shape incision.
Dislocation: by external rotation
Closure: In layers capsule rarely closed. Fascial planes are closed and skin
The advantages of this approach include preservation of the vascularity, stability following the procedure with less chance of dislocation. Limited morbidity, high stability and with good access to the acetabulum are key advantages of this approach.  The approach limits muscle cutting and separation, reduce chance of dislocations, and makes it easier to take intra-operative radiographs as the patient is supine in position. Key muscle groups the extensors and the abductors are kept intact the along with the medial circumflex femoral artery and it’s branches. , 
The key limitation of this approach is the limited access making it technically demanding to place components in arthroplasty. Even though the approach to the acetabulum is good approach to proximal femur is limited through this approach. Some encourage to use a fracture table to get a better approach to the femur  while others use the standard operating table. 
Even though many total hip arthroplasties and even resurfacing hip replacements are done using this approach  due to limited access and technical demanding nature  this may not be a popular approach among arthroplasty surgeons.
Specific complications, 
Damage to lateral cutaneous nerve and the anterior cutaneous nerve should be kept in mind. 
Common surgical procedures
Modifications to the approach
The modification of this approach includes two incision direct anterior approach and minimally invasive direct anterior approaches. ,  Low blood loss, early recovery, early mobilisation reduced operating time are the advantages of the minimally invasive anterior approach. 
5. Antero-lateral approach (Watson-Jones)
Described initially by Watson-Jones  approaches the hip between tensor fascia lata and the gluteus medius muscle planes.
Position: The patient can be positioned supine or laterally on the table
In the supine position a sand bag may be placed under the pelvis on the operating side.
Incision: Longitudinal incision is made while flexing the hip slightly extending over the centre of the greater trochanter running posteriorly along the shaft of the femur.
Soft tissue dissection: This is done by identifying the plane between the tensor fasciae latae and the gluteus medius taking care not to damage the inferior branch of the superior gluteal nerve as it supplies the former muscle.
Vastus lateralis is identified and the muscle is detached from the origin and the capsule identified.
Internervous plane: Since the superior gluteal nerve supply both gluteus medius and tensor fasciae latae it is difficult to define a true internervous plane for this approach. However as long as the plane between these muscles are not dissected superiorly up to the origin the nerve will remain intact.
Arthrotomy: The capsule is divided longitudinally over the anterior superior femoral neck.
Dislocation: This is done by applying external rotation, traction and adduction to dislocate the hip.
Closure: The wound is closed in layers starting with the capsule. If a trochanteric osteotomy is performed it has to be re attached.
The key advantages of the approach include stability, less chance of posterior dislocation, less risk to sciatic nerve damage unless during dislocation where traction can stretch the nerve. Precautions should also be taken not to damage the superior gluteal nerve.
One of the key limitations is that possibility of abductors getting weak during dissection or by denervation of the nerve supply. 
Damage to superior gluteal nerve and lateral circumflex femoral artery (LCFA) should be kept in mind.
Damage to the femoral nerve and vessels are a relatively rare complication.
Mueller modified the approach to avoid trochanteric osteotomy.
Another recent modification for this approach is the minimally invasive approach. Antero lateral minimally invasive approach (ALM) has been described as a good alternative  to traditional approaches as it reduces hospital stay, surgical time, blood loss, morbidity, and encourages early mobilisations, and recovery. Even though some report high complication rates  with this approach over all this is an approach with many advantages in the modern day practice. However this is a technically demanding procedure that needs expertise.
Trochanteric flip approach developed by Ganz et al is can be considered as a modification or combined type approach where steps of posterior approach is used but the hip is dislocated anteriorly by performing a trochanteric flip osteotomy.
The key advantage of this approach is the protection of medial circumflex femoral artery thus preserving the main blood supply to the hip. Therefore this becomes an important approach to use in conservative hip surgery and the surface replacement of the hip joint as this can protect the femoral head and neck from developing avascular necrosis (AVN).  The key step of this approach is the trochanteric flip osteotomy where a bony flip of around 1.5cm made over the greater trochanter and reflected anteriorly along with vastus lateralis, gluteus medius and minimus and the hip is dislocated anteriorly thus avoiding and dissection of short external rotators.
The key limitations include the patient need to be non-weight bearing for six weeks or until the trochanteric osteotomy is healed. Non-union and separation of the osteotomy are other potential complications.  (Fig 4)
6. Direct lateral approach
Direct lateral approach also called as the trans-gluteal approach initially described by Kocher in 1903  popularised by Hardinge in the modern age  gives good exposure to the hip joint preserving most of gluteus medius minimus and vastus lateralis, and the vascularity. It exposes the femur well with good access to the joint.
Position: This can either be done on lateral or supine position
Incision: from mid point of greater trochanter longitudinally along the femoral shaft extending around 8-10 cm with proximal extension up to anterior superior iliac spine. 
Incision: Usually it is made about 7-10 cm below the tip of the greater trochanter along the anterior border of the femur.
Soft tissue dissection: Gluteal fascia and illio tibial band divided and plane between tensor facia late and gluteus maximus is identified. Gluteus medius incised and approach via gluteus medius and vastus muscles.
Internervous plane: As the gluteus medius tendon and muscle fibres and the vastus lateralis muscles are split there is no true internervous plane. However it is important are split protect the superior gluteal nerve by making the incision distal to the point which it enters the muscle.
Dislocation: Leg can be externally rotated and abducted for dislocation .
Closure: Illio tibial ligament initially re attached followed by gluteus medius suturing.
This approach gives good access to the hip and yet preserves vascularity and minimise risk of damage to sciatic nerve as compared to the posterior approach.
Damage to gluteal muscle mainly medius can increase recovery time,
Complications are relatively rare with low dislocation rates. Heterotopic ossification may be a problem in selected cases. 
Common surgical procedures
Total hip replacements, hip resurfacing,  trauma, and many procedures can be done via this.
Modifications include the trans gluteal approach.  This has been compared with Watson Jones approach and appear to be a good alternative to the traditional approach.  According to some authors the surgical exposure can be improved by modifying the way muscle fibres are split, fascia is cut retractors are placed and closing the wound. 
Lateral trans trochanteric approach was initially described in 1881 by Ollier and popularised by Sir John Charnley provide a good exposure hip joint is mainly used in revision arthroplasties. 
7. Posterior approach
Also called, as the Southern approach is one of the commonest approaches used by the orthopaedic surgeons at present.
Position: Mostly done in lateral position
Incision: standard incision is 10-15 cm long curve-linear extending from posterior superior iliac spine to greater trochanter and extending down in a variable distance along the shaft of the femur. The modern incisions are shorter than the standard. As this can be extended if needed it is sensible to initially make a smaller incision and extend if needed.
Soft tissue dissection: Initially fascia lata and vastus lateralis is cut. The gluteus maximus fibres are split. Then the hip is internally rotated and short external rotators are cut after holding them with stay sutures.
Obturator internus and piriformis is detached and reflected backwards to protect the sciatic nerve.
Internervous plane: As we split through the fibres of gluteus maximus rather than between muscle planes it is difficult to find a true internervous plane. How ever as the nerve enters the muscle medial to the split the muscle denervation is unlikely.
Arthrotomy: Capsule is incised with a T shaped incision
Closure: Capsular closure is described but the practicality is an issue mainly following hip arthroplasty procedures.
It is important re-attached the external rotators and obturator internus and piriformis.
This is a good approach that provides excellent exposure to both acetabulum and the femoral head and neck equally making it easier to surgical procedures well.
Due to the possibility that blood supply may get damaged resulting in AVN has limited it’s used in conservative hip surgery such as open hip debridement, open surgery for hip impingement and use of this in paediatric population is not recommended.
The posterior approach has specific complications these are
Damage to sciatic nerve, which could be either stretching which recover usually, or permanent damage, which will result in a foot drop.
Damage to inferior gluteal vessels, branches of profunda femoris vessels and rarely femoral vessels.
Invariably branches of medial circumflex femoral artery are cut during this approach, which can theoretically give rise to AVN of femoral head and neck. This does not matter in total hip replacement as the head and neck is removed but in conservative procedures including hip resurfacing arthroplasty. Many authors have challenged however the clinical implications of this blood flow drop. -  Some argue the blood supply drop is transient which may recover during post-operative period. 
Common surgical procedures
This is in an approach commonly used to do Primary and revision total hip replacements, hip resurfacings, and other procedures such as open reduction of hip dislocations and fixation of acetabular fractures.
Minimally invasive (MIS) posterior approach is a modification. This approach when compared with standard lateral approach has similar outcomes during early post-operative period such as surgical duration, blood loss and hospital stay but long term results such as Harris Hip score is higher in the MIS.  Similar results have been achieved when compared with postero-lateral approaches.  When compared with the standard posterior approach it was found to be less blood loss, less post-operative pain and early recovery.  Gibson approach  is another modification and can be considered a poster-lateral type of approach.
8. Postero-lateral approach
Initially described by Langenback in 1874  is another approach that can be used in hip arthroplasty surgery. Compared with trans trochanteric approach it is believed that this has less blood loss and shorter hospital stay. 
6.Medial approaches are mainly used developmental dysplasia of the hip, in young patients and children as it protects most soft tissues and blood supply to the hip joint.
The medial approaches can be further sub classified to antero-medial, postero-medial (Ferguson) and Ludloff’s approach
The minimally invasive approaches to the hip joint used in hip arthroplasty.
Due to ion crease blood loss, slow recovery increase intra operative time, and delay in discharge more and more orthopaedic surgeons have been keen to develop minimally invasive approaches. These are usually modifications of existing approaches so that a surgeon preferring a certain standard approach can try the minimally approaches. The commonest minimally invasive approaches are minimally invasive antero lateral, minimally invasive direct lateral  minimally invasive posterior, minimally invasive anterior
The principles include shorter skin incision either single or multiple, minimal soft tissue dissection, without compromising the access or the quality of the surgery.
The reasons for developing Modified and modern approaches to the hip joint was mainly driven by the concept of minimal invasive surgeries being developed through out the surgical fields as they are supposed to be less invasive with low intra-operative complications such as low blood loss, less tissue dissection and less operative time, with early recovery, early mobilisation and early discharge from hospital. With development of smaller implants better instrumentation, better pre-operative planning, use of navigation, and better intra-operative imaging it has been possible to develop and use minimally invasive approaches to major surgeries like total hip arthroplasty or revision hip surgery. How ever at present there is debate over the long term out comes quality of surgery including implant positioning and learning curve for minimally invasive approaches over standard surgical approach. The answers to these questions will come from the research done comparing minimally invasive approaches versus the standard surgical approaches.
In conclusion it is important note that there are multiple surgical approaches to the hip joint and some better suited for arthroplasty and some for more conservative hip surgery. A checklist of factors one should consider before an approach is selected is,
What type of surgery? Is it conservative or hip arthroplasty?
If is arthroplasty, is it Total hip replacement, Hip resurfacing or a Revision hip replacement?
Age of patient? Adult young adult or a child
What part of the hip do you need the best exposure to? Acetabular socket, Femoral head and neck or both
Surgeon’s preference and competence in doing the approach.
Whether the surgery is elective or trauma/emergency.
The relationship between the outcome of surgery and the surgical approach is still less understood, even though many comparison studies have been done.   The final decision on what surgical approach to use is a clinical decision that has to be made by the operating surgeon.