Total hip replacement- Symbios custom hip

As with all hip replacements planning is crucial.
This image is a pre-operative long leg radiograph demonstrating advanced osteoarthritis in the left hip with joint subluxation, a shallow acetabulum, a short leg and a deformed proximal femur. This woman in her early 20s had childhood hip septic arthritis with multiple washouts and later multiple circular frame interventions. She also has advanced degenerate changes in her left knee with an almost ankylosed joint.
Planning begins in clinic with an initial decision about whether the hip can be reconstructed with an off the shelf implant. Templating software may help with this decision.
In this case the proximal femoral anatomy is too deformed to accommodate a standard femoral stem and hence the decision for a custom implant.

Pre-op AP pelvic radiograph shows a significantly dysmorphic hip with a shallow acetabulum, shortening and an abnormally shaped proximal femur.

Lateral radiograph of the left hip in the same patient. In addition to the deformity the bone is osteopaenic.

Once a decision has been made to use a custom stem a CT scan is required. Each company has their own protocol. Usually the pelvis, both hips, both knees and both ankles are imaged.
I begin the planning process by assessing the acetabulum, using both the plain radiographs and the CT scan. Some of the key questions include:
Is there enough bone for reconstruction?
Does residual metalwork need removing? Should this be in one or two stages?
Is the centre of rotation changing?
High or low acetabulum?
What effect on leg length will this have?
Does any further kit need ordering: augments for a shallow acetabulum; small size cups if the true acetabulum has limited bone stock?
In this case restoring the true anatomic hip centre is achievable with a 42mm hemispherical cup. The planned cup position is shown in the segmented CT images. The desired inclination (usually 45 degrees) and version (usually 20 degrees) can be planned, taking into account the designed stem version, native acetabular version, pelvic tilt and bone stock.
The red hemisphere shows the planned cup position and gives an idea of how much bone will be removed during reaming (slide 26).

Surgical prescription and leg length correction
Once the cup is planned leg lengths can then be re-assessed and either lengthened or shortened via the stem position and design.
In this patient the left hip is short by 39mm using the greater trochanters as a reference point and 58mm using the lesser trochanters (remember the left is deformed secondary to infection and multiple surgeries). The rest of the femur is also abnormal and her leg lengths will not be restored with a hip replacement alone. Patients often need this telling to them multiple times.
In extreme cases where the leg length cannot be restored, lengthening can be performed away from the hip using a Precice nail or circular frame at a later date.

Measuring leg length discrepancy
It is also important to consider pelvic or spinal abnormalities that may contribute to an apparent leg length discrepancy, as well as the rest of the lower limb. This needs to be considered at the planning stage and may influence the desired corrections. Always ask the patient the difference they feel as this provides a clue to the apparent leg length discrepancy.
The total leg length difference (not just at the hip) in this patient is 34mm.

The CT scan is also used to work out the optimum size and shape of the custom femoral stem. The stem design can be tinkered with to allow maximal metaphyseal fixation.
Once the optimal position is achieved the resection level is then calculated. The femoral neck osteotomy level is planned at 32mm from the tip of the greater trochanter (C), or 40mm from the most superior point of the femoral head (D). Usually the distance from the lesser trochanter is also measured, as this is an easy landmark to identify intra-operatively) but in this case it is not obviously identifiable.

The planned uncemented stem should fill the metaphysis in the proximal femur to maximise the bony contact and encourage osseointegration – ‘fit and fill’.

Stem design and fixation
Further CT segments demonstrate bone quality, geometry and rotational profile.
The uncemented stem can be manufactured with either a partial or full hydroxyapatite coat. In more osteopaenic bone I prefer a fully HA coated stem.

A 12-14cm skin incision for the posterior approach is made in line with the femur distally and then curves posteriorly towards the iliosacral joint at the proximal end. The patient is prepped with 2% chlorhexidine and draped. The incision for a posterior hip approach is marked (slightly posterior to the greater trochanter) and an Ioban (iodine impregnated) adhesive dressing applied. A large one is used on the lateral thigh and a smaller folded one on the medial thigh, covering all exposed skin.
There may be multiple previous incisions, which can be ignored or incorporated depending on their location.
The length of the incision depends on the size of the patient and the anticipated degree of difficulty of reconstruction. . In an obese patient or where lengthening is planned a longer incision may be necessary for exposure and to release tight structures.

The fascia lata is identified beneath the fat and incised with the diathermyDistally the fibres of vastus lateralis are uncovered; proximally the fibres of gluteus maximus are split either by hand or by blunt dissection.
Straying too far posteriorly can mean there is more gluteus maximus muscle in the way. In obese patients keep re-evaluating where the greater trochanter is and adjust your approach if necessary.

The gluteus maximus muscle is split proximally, then the trochanteric fatty / fascial layer is divided before the external rotators can be clearly visualised, using a swab to sweep posteriorly.I then use the Mayo scissors to bluntly dissect and identify the nerve inferior to the piriformis. It is encased in a fatty envelope and finding this often gives you a clue to the nerve’s location.
The sciatic nerve is at risk during a posterior approach to the hip. I routinely palpate and then expose it before placing the Charnley bow retractor.
Placing the patient’s foot on the scrub nurse’s Mayo table helps internally rotate the hip bringing the sciatic nerve further into the operative field.
The sciatic nerve exits the pelvis through the lower part of the sciatic notch. The nerve appears below the piriformis muscle and lies over superior gemellus, obturator internus, inferior gemellus and finally the ischial spine.

A Charnley bow retractor is carefully inserted after identification of the sciatic nerve, the anterior curved blade is placed under the anterior fascia lata, the posterior ‘squared’ blade is placed under the posterior edge of fascia lataTake care not to catch and damage the sciatic nerve that has already been identified.

The short external rotators and capsule are taken down with the diathermyThe trochanteric bursa is removed to identify the piriformis and short external rotators. A Lagenbach retractor is useful to move gluteus medius anteriorly to aid in piriformis identification.
A sharp Hohmann retractor is placed superior to the piriformis tendon and the Lagenbach removed. The assistant can then further internally rotate and flex the hip to put the tendon under tension.

The piriformis tendon is tenotomised as close to the femur as possible. The other short external rotators are similarly detatched from their distal insertion on the greater trochanter. These include the superior and inferior gemelli and obturator externus. The quadratus femoris can be released with the diathermy if further exposure is needed.

There is normally an abundant blood supply to the capsule and short external rotators and bleeders should be dealt with on the way in to the hip.

An L-shaped arthrotomy is made, starting proximally at the edge of the acetabulum just above the superior edge of the piriformis, heading towards the tip of the greater trochanter, once the short external rotators are releasedIt is continued distally along the edge of the femoral neck until the quadratus femoris muscle is reached.
The head and neck of the femur should be visible. Ensure the capsule from the inferior neck is released for an easier dislocation.
If significant lengthening planned the gluteus maximus tendon can be partially or completely divided.

The hip is dislocated with flexion, internal rotation and adduction.In stiff and multiply operated hips ensure the capsule, scar tissue and large posterior osteophytes have been sufficiently released. Be careful if your assistant is over-zealous as an iatrogenic fracture can happen at this stage. An in-situ neck cut can be done if dislocation is not possible.
The remnants of piriformis can be removed from the piriformis fossa on the femur along with any residual capsule that is in the way of the proposed neck cut.

The neck osteotomy level is marked as per the pre-op plan and a sharp osteotome is used to begin the osteotomy at the planned levelI print out the custom plan and stick it on the wall so it is available as a reference tool during the surgery. The plan provides accurate guidance on the osteotomy level and this can be measured from both the greater and lesser trochanters using a short ruler.
See slide 6 for the proposed neck resection point.

The osteotome marks the site for the planned neck resection. Slide 7 shows the landmarks that can be used to ensure an accurate cut. It should be perpendicular to the femoral neck and guide the surgeon in the next step whereby the osteotomy is completed with the saw.

The neck osteotomy is completed with an oscillating saw and the femoral head is removedCare is needed to not damage the greater trochanter, particularly if it is overhanging or abnormal. If this is the case the cut can be done in a step manner with a vertical limb just medial to the greater trochanter.
The cut should be perpendicular to the femoral neck with Hohmann retractors anteriorly and posteriorly protecting the soft tissues.

The femoral head is removed
It can be gently levered out using a broad osteotome if there is no remaining capsular attachment

The head is a source of autologous bone graft, which can be useful in complex cases where bone graft is required.
The image demonstrates a large area of subchondral collapse secondary to avascular necrosis of the femoral head.

Adequate exposure of the acetabulum is ensured by precise retractor placement, placing a sharp Hohmann retractor anteriorly and another one inferiorly.The inferior one can be tied to the Charnley retractor using a large swab, to free up the assistant’s hands.
The acetabulum needs to be exposed circumferentially. This involves removing any remaining labrum or soft tissues. Keeping the scalpel within the acetabulum should reduce inadvertent soft tissue injury.
If the exposure is difficult the reflected head of rectus femoris can be released from the anterosuperior margin of the acetabulum using a scalpel. This should allow further excursion of the femur anteriorly (and thus out of the way).
Finding the true acetabulum is required if an anatomic reconstruction is planned. The inferior Hohmann needs to be carefully placed below the transverse acetabular ligament. This is the lower most border of the acetabulum. Dissection and soft tissue clearance superiorly will expose the location of the true acetabulum.
The transverse acetabular ligament is also useful to confirm version and aid in cup positioning and alignment.
Structures at risk include the superior gluteal artery and nerve – they emerge above the piriformis through the greater sciatic foramen. The deep branch supplies the abductors and limits the amount of superior retraction and exposure towards the iliac crest.
The femoral nerve is also potentially vulnerable anterior to the acetabulum if the Hohmann placement is in the soft tissues. Dissection of the soft tissues off the anterior acetabulum will create a pocket for the retractor to be placed into minimising the risk.

Any remaining capsule and labrum are excised along the rim of the acetabulumA self retainer is placed in the superior part of the wound, again making sure the short external rotators and capsule are reflected posteriorly protecting the sciatic nerve.
Foveal ligament remnants can be removed or reamed out in the next step.

Initial acetabular reaming is focused on medialisation to the level of the medial wall as defined by the condyloid notch, directing the reamer straight down.Take care with soft bone or sharp reamers.
The pre-op CT and custom plan will give you an idea of how much bone needs to be removed to adequately seat the socket and get to the true floor (See slide 4).
I use the smallest reamer (36mm) where the socket and is small and shallow. Once I reach the true floor subsequent reaming is performed in 2mm increments. This debrides the articular cartilage and exposes the subchondral cancellous bone. The size of the cup is determined by the largest reamer that will result in a tight press-fit between the anterior and posterior walls and columns. Again the pre-op plan will guide the surgeon – it is not uncommon to be one size (2mm) up or down.

After identifying the anatomic hip centre and medialising, the remaining reaming should be in the desired cup orientation, usually 40-45 degrees of abduction and 15-25 degrees anteversionThe size of the cup determines the liner and head size and hence jump distance (the distance the head travels prior to dislocation).
In dysplastic hips a 28mm or 22.225mm head may be the largest possible. Where the acetabular anatomy is not dysplastic I prefer to use a 32 or 36mm head, which increases the head:neck ratio and jump distance, and reduces the risk of dislocation
In this patient the acetabulum is reconstructed anatomically in a more distal position (where it should or used to be). This is my preference as the bone stock is usually better, complication rates are lower and it is easier to restore leg lengths. Extra small components or superior augments are occasionally needed. Hence the importance of the planning – it is too late now if they are not available.

The desired position of the cup is usually 40-45 degrees of abduction and 15-25 degrees anteversion. This may vary in the more complex cases depending on other fixed anatomical points: pelvic tilt, concurrent spinal deformities etc.
To assess the cup version I use the transverse acetabular ligament, which is a fairly consistent patient specific soft tissue landmark. In most cases placing the inferior part of the cup parallel to the TAL will recreate the correct anteversion. Having the planning CT is also handy as it demonstrates the amount of bone coverage which again visually confirms how the cup is meant to sit. If the patient is positioned perfectly parallel to the floor then operative anteversion can also be assessed using the introducer. In this way the inclination can also be estimated.

Subchondral bleeding cancellous bone should be exposed

The hemispherical uncemented press fit ‘April’ cup is impacted, following which screw augmentation is possible.The April press fit cup from Symbios is porous titanium and HA coated. A poly or ceramic liner is available. My preference in patients under 40 years is a ceramic liner and a ceramic head.
Using the same manufacturer for hard on hard bearings is recommended in all cases.
The minimum socket size for a 36mm head is 52mm, with either a ceramic or poly liner. The April socket goes down to size 42mm. For smaller sockets I use the DePuy Bantam uncemented socket which starts at 38mm. At this size only 22.225mm metal heads and poly liners are available.
Trials sockets are available and can be used to check the acetabular fit and orientation. I do not routinely use them as I find the feedback from the last reamer provides enough information at this stage.

I tend to only use supplemental screw fixation in a primary case where there is pre-existing deficient bone. In this case the acetabulum is flat and despite medialising the socket there is not complete bony coverage, hence the screw insertion.
Where additional primary fixation is needed at least 2 screws should be inserted in the posterosuperior ‘safe zone’.

The acetabulum can be divided into 4 quadrants by imagining a line from the anterior superior iliac spine to the centre of the acetabulum, and a second line perpendicular to this. This creates a ‘safe zone’ for screw insertion.
Safe zone(posterior-superior): A relative term. The sciatic nerve as well as superior gluteal nerve and vessels are potentially at risk here.
2: Screws here should be no more than 20mm in an average adult. Proceed with caution.
3: Obturator neurovascular bundle at risk. Avoid fixation
4: External iliac artery and vein at risk. Avoid fixation

The screw is held with a holder whilst being positioned and then advanced using a flexible screwdriver.
The screw holder should be released once the screw begins to advance

The ceramic liner needs to be inserted and impacted carefullyI find it easiest to insert and advance the liner by hand and ensure it sits flush to the face of the cup. Once the orientation is satisfactory and the taper is engaged, the liner can be impacted with the appropriate size impactor.
Trials liners are also available but there are no lipped or offset liners available in ceramic at this size. Hence the insertion of the definitive implant.

The proximal femur is brought in to view with flexion, internal rotation and adductionA small swab should be placed in the acetabulum to protect the ceramic liner from damage and then attention directed towards the femur.
A femoral retractor under the femur presents the femoral neck and protects the skin from the sharp rasp. Make sure the retractor sits on the bone and not the soft tissues as the sciatic nerve is close by.

A box chisel is used to enter the femoral canal. The starting point is crucial – it should usually be posterior and lateral in the proximal femur (in the piriformis fossa).This offers best access to the femoral canal in both AP and lateral planes.
In patients that have had previous proximal femoral surgery this relationship may be different and both radiographs and the pre-op CT scan will aid in entry point identification. The entry point in this patient is more medial than the piriformis fossa.
Previous surgery often makes femoral preparation more difficult. There may be sclerotic bone or obliteration of the canal. In this case the image intensifier, a sharp starter drill and / or flexible reamers may be needed before rasping. Retained metalwork is not uncommon in young patients and appropriate kit and imaging may also be required. I prefer to remove the metalwork and do the hip replacement in one sitting. Occasionally the metalwork is very difficult to remove and the procedure should be staged.

After the box osteotomy is made in the femoral neck the custom rasp is gradually impacted.Whilst it is sharp care must be used, particularly with poor quality bone, as there is a risk of a calcar fracture.

The custom rasp tends to find its own way as it follows the geometry of the proximal femur. Dialling in any further version is not necessary and may cause an iatrogenic fracture.An introducer screws on to the shoulder of the rasp and this is used to gently hammer the rasp in. Gentle controlled blows are performed to minimise the risk of an iatrogenic fracture.
The rasp and definitive stem have identical geometry.

Once the rasp is seated to the planned level a trial head can be attached and the hip reduced.In the more complex cases I tend to aim for the largest head size possible to reduce the dislocation risk. This is determined by the cup size and it is worthwhile checking with the implant company the options available at different sizes. This patient has a small acetabulum and a 28mm is the largest head that is compatible with a 42mm cup.

Stability, leg length and soft tissue tension should be assessed as you would do for any hip replacement, after trial reduction.To reduce the hip I ask my assistant to provide traction with the knee flexed at 90 degrees and the hip flexed at 30-40 degrees. I use my finger to sweep the posterior soft tissue out the way and ensure there is no block to reduction. It also re-assures me that the sciatic nerve is out of the way. With my other hand I use the head pusher to reduce the hip, while my assistant simultaneously rotates the leg back on to the operating table. A skid can be used if the reduction is difficult (if the leg has been significantly lengthened for example) but care needs to be used to avoid scratching the ceramic bearings. I wrap a swab around the metal skid to minimise this (or try and avoid using it).
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Leg lengths can be tested and compared to the pre-operative length, taking into account the planned correction.
A shuck test with the hip in neutral will confirm appropriate soft tissue and abductor tension. I place one forearm under the flexed knee and abduct the leg to a neutral position. With my other hand I place two fingers around the femoral neck and distract the leg. In the same position the hip can also be pulled laterally (towards the ceiling) to assess abductor tension. The books quote 5mm as acceptable but this variable depending on the specifics of the procedure. If lengthening has been performed or offset increased this may be tighter than the usual 5mm.
Full extension and external rotation checks for anterior instability (rare with a posterior approach); flexion to 90 degrees and gentle internal rotation checks for posterior instability. This is the commonest direction of dislocation – I like to have 60 degrees of internal rotation at 90 degrees of hip flexion to be satisfied.
Using a custom femoral stem means there are fewer options to play with at this stage if instability is identified. Offset and leg length can only be adjusted to a certain extent with differing neck lengths and this is predominantly for fine tuning. Meticulous pre-operative planning should however mean that larger adjustments are not necessary. If there is concern at this stage the acetabulum can be re-positioned to compensate. If the articulation is large enough a dual mobility or constrained liner are other options, but are likely to have an impact on wear in younger patients.

The trial rasp is removed and the definitive stem inserted in the same mannerAgain gentle blows with the hammer are used to insert the stem to the desired level.
The definitive stem is HA coated and tends to accurately sit at the same level as the rasp. The lateral shoulder on the implant prevents it being inserted too distally.

The trunnion should be cleaned and dried before the ceramic femoral head is carefully impacted on the trunnion and with one blow.The definitive stem is HA coated and tends to accurately sit at the same level as the rasp. The lateral shoulder on the implant prevents it being inserted too distally. Care is needed as this does introduce the risk of an iatrogenic calcar fracture. If this occurs and the implant continues to have good metaphyseal hold then cerclage cabling is all that is required.

Final check for stability after reductionStability tests are repeated.

Four Ethibond sutures with double throws are inserted through the short external rotators and the capsule for an Enhanced posterior capsular repairThe most proximal should capture both the piriformis tendon and the underlying capsule. The remaining three ideally capture any remaining capsule and the rest of the short external rotators. A clip is applied to each.
The sciatic nerve is checked again before closure.

Drill holes are made in the greater trochanter and a suture passer used to pull the Ethibond sutures through.
After each of the four drill holes are made the sutures are pulled through and held with clips.

The sutures are then tied to obliterate the posterior dead space and form a posterior pseudocapsule
The top two sutures are tied together over the bony bridge whilst the assistant reduces the tension by elevating the knee. The bottom two are similarly tied.
The risk of dislocation is reduced with an intra-osseous enhanced posterior repair

The fascia is closed with Vicryl, followed by the fat and skin.

A subcuticular dissolvable monocryl stitch is used for the skin
Prior to closure local anaesthetic is injected into the capsule and soft tissues.

Steristrips and a dressing applied

Post-operative AP radiograph
Both stem and cup are in the planned position and leg lengths have been much improved. There is good metaphyseal fit and fill around the stem. The lateral shoulder on the implant abuts the lateral cortex adding to the primary stability.

Post-operative lateral radiograph