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Microport Intracapsular Total Hip Replacement

    Overview

    Learn the Microport Intracapsular Total Hip Replacement surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Microport Intracapsular Total Hip Replacement surgical procedure.
    Traditional approaches to Total Hip Replacement , Trochanteric Osteotomy, Anterolateral, Posterior and more recently Anterior have one thing in common; they involve cutting of the anterior or posterior capsule and significant rotation of the leg to effect dislocation and access. There is no doubt that preservation of the capsule and avoidance of excessive rotation greatly reduce post-operative pain and increase stability.
    In recent years the anterior approach has become more popular but the learning curve is long, orientation unfamiliar and extensile manoeuvres complex. As a more mature surgeon I wanted the immediate benefits of this approach without the difficulty. I became aware of the SuperPath Approach which was a development of the Supracapsular Approach and went to watch surgeries with Jimmy Chow in Phoenix and Mike Cronin in Warwick; thank you both.
    Over a learning curve of about fifteen patients with the Microport total Hip replacement I felt that a second portal for acetabular reaming and cup positioning was not necessary in all cases. I essentially started using a single incision Supracapsular approach for the Microport intracapsular total hip replacement which is described in my operative technique that follows.

    Indications

    Indications for the Supracapsular Approach are essentially the same as for regular THR. If patient habitus suggests a large exposure is required or if metalwork has to be removed, then the surgeon’s default technique is advised. The tecnically easiest cases are those with a high offset or shallow sockets. The beauty of this approach is that it can be easily extended into a conventional posterior approach if access is poor with no functional detriment to the patient.
    Ideal candidates for this type of surgery are patients wanting rapid painfree mobilisation or those with potential instability issues
    Favourable radiological features are high femoral offsets and slightly shallow sockets; both these features aid femoral preparation.

    Setup

    Operation – 1

    The patient is setup in a regular lateral decubitus position with sacral and pubic props.
    The only difference from a regular posterior approach is the absence of a pillow between the knees and flexion of the hip beyond 45 degrees resulting in slight adduction of the femur.

    One caveat to be aware of with this set up is that if the hip is too flexed, the sciatic nerve will be in closer proximity to the posterosuperior border of the acetabulum.

    Remarkably few instrument trays are required.
    Angled retractors, femoral rasps, narrow reamer stalk and cup adapter screw with trials

    Basic tray with reamer stalks, cup impactor and modular liner impactors

    Basic Tray with angled retractors and modular necks

    Tray with modular trial heads and necks.

    Basic Tray with rasp/stem holder, curved rasp, modular neck holder and modular cup adapter

    This is the curved rasp which can be used to lateralise the initial femoral aperture after the initial itramedullary drill entry.

    This is the reverse gouge which is used the expand the metaphysis and remove bone from the femoral head prior to initial rasp insertion.

    This is the trial modular neck holder

    The right angled retractractors give excellent exposure of the femoral neck and make life easy for the assistant but should only be inerted/postioned around the neck once the capsulotomy has been performed.
    Earlier insertion could lead to neurovascular compression or injury.

    This is the “U” shaped initial chisel; this is used straight after the primary end cutting drill to widen the aperture at the trochanteric/notch neck junction.
    The cutting blade sometimetimes rotates so a fixed box chisel is also on the set which can be used to determine anteversion of subsequent femoral reamers.

    The skin incision is referenced to the greater trochanter which is palpated through the soft tissues with the hip flexed and adducted as described.
    Essentially the incision is the proximal limb of a regular posterior approach . For the single incision technique I start about 2cm distal to the greater trochanter and extend 6-8 cm in a cephalad direction. A Charnley type retractor is not required but Travers or Norfolk & Norwich type superficial and deep retractors are ideal.

    Once the skin incision is made, a cutting diathermy is preferred through the fat layer and investing tissue over Gluteus Maximus (G.Max) . The fibres of G.Max are opened with blunt dissection and placement of a deep spreader reveals a fatty bursa and then Gluteus Medius.


    Gluteus Medius is retracted anteriorly revealing the Piriforis tendon posteriorly. When this interval is defined the capsule is exposed and the operation which is entirely intracapsular takes place in this space.
    There is a temptation to use Hohmann type retractors before the capsulotomy is performed; this should be avoided as the Sciatic Nerve is close by posteriorly and can be compressed if these retractors are used extracapsularly.

    Using a cutting diathermy, the capsule is exposed starting at the tip of the trochanter and coursing through the trochanteric fossa along the femoral neck. Once over the head feel for a bump as the diathermy hits the acetabular rim and continue proximally for about 10 mm. Cutting any more proximal is becoming dangerously close to the sciatic nerve especially if the hip is flexed more than 45 degrees.
    The assistant should be holding the foot continuously at this stage monitoring for (and warning about) any signs of sciatic stimulation.

    Homan type retractors should not be used until the femoral neck has been identified intracapsularly. The anterior retractor is placed first followed by the posterior; it is worth chechecking that the posterior retractor is approximated to the neck and truly intracapsular; this is another opportunity for neurological compression !

    Once the capsule has been divided, angled retractors can be safely place anteriorly and posteriorly around the femoral neck- ensuring they are intracapsular. It may be helpful for the assistant to abduct the leg at this stage to facilitate retractor placement.

    The femoral canal is entered via the trochanteric notch with an 8mm drill like the initiall stages of a femoral nailing.

    The integrity of the canal is confirmed with a feeler guage.
    If there is any doubt the back-facing rasp can be used to confirm.

    The aperture to the canal is widened using a U-shaped chisel.
    Place the chisel on the femoral head close to the acetabular rim aiming for the medullary cavity. The chisel is advanced removing bone from the lateral part of the femoral head and cancellous bone from the metaphysis.
    This manoeuvre is repeated maybe two or three times until there is sufficient room to admit the first femoral rasp. A rat-tailed rasp is advised to remove lateral cancellous bone towards the greater trochanter; attention to detail at this stage prevents varus implant positioning.

    The lateral entry point can be enlarged with a gouge or a rat-tailed rasp

    An alternative for enlarging the entry point is to use the Rat-tailed rasp

    Femoral preparation commences with the smallest number 1 rasp.

    It is important to determine the anteversion at this stage. This can be done in two ways; referencing from the tibia or from the native femoral neck which is still intact. In practice, awareness of both is ideal.
    Failure to appreciate the correct version can result in loss of stability or edge wear.
    As with all THRs it is important to fine tune sicket version relative to femoral component positioning.
    The aim of the rasping is to prepare the the femur for the appropriate stem size as indicated by preoperative templating but fine tuned intraoperatively.

    Operation – 2

    The rasp is driven into the femur til tight; The final depth is determined by templating relative to the tip of the greater trochanter; this is in the region of 18mm and can be confirmed either with the feeler guage or mar markings on the rasp holder.

    Implant version has been discussed but leg length is equally critical.
    In other approaches the lesser trochanter is visible and the level of neck osteotomy is referenced from this landmark. For the intracapsular approach the Greater Trochanter is referenced. Preoperative templating reveals the distance between the shoulder of the femoral trial selected and the tip of the Greater Trochanter; this is measured intraoperatively using the calibrated ‘feeler guage’ inserted into a dimple on the shoulder of the trial and noting the depth from the tip of the Greater Trochanter; this is usually in the region of 18mm.

    Once the correct size trial has been seated to the correct depth, the femoral neck osteotomy can be performed. It is of paramount importance the retractors around the femoral neck are completely intracapsular. Harm can be done if the retractors are malpositioned.
    Once satisfied with retractor and trial placement an oscillating saw with relatively thin blade is used to perform the osteotomy commencing the cut against the shoulder of the trial. If a wider blade is used there is not enough space to perform this.
    Rotation of the leg will confirm that the osteotomy is complete.

    Two Schantz Pins are drilled into the femoral head. The first is drilled into the head close to the superior rim of the acetabulum; this is then used to angle the head and a second pin is inserted. Sufficient leverage can now be exerted on the head to pull it out of the wound. Occasionally the legamentum teres is very strong and a skid may be needed to apply further leverage. If difficulty is still encountered then the head can be sectioned and removed piecemeal.

    Once the head has been removed, it can be inspected to check the level of the neck osteotomy.
    At this stage an assessment of the femoral head diameter can give an initial indication of cup size.

    Re-check the osteotomy cut and depth of femoral trial.
    If the neck cut looks too short relative to the templating one can recheck the distance from the shoulder of the trial rasp to the tip of the trochanter- this is usually about 17mm. One can then reassess the depth of the trial rasp and if necessary re-cut.

    To aid acetabular exposure the leg is placed in a less flexed position- probably 20 degrees at the hip.
    The deep retractors are positioned so that they retract the capsule anteriorly and posteriorly but leave the labrum exposed. They should not be under too much tension.
    Additionally, Judd nails can be positioned if soft tissue is interfering with the exposure (as seen here).

    The Superpath reamer stalk is very thin and this allows better access to the acetabulum than conventional or angled reamers.

    I have found that for the majority of cases, a second incision to facilitate the Superpath technique of acetabular preparation is not required. However, using a single incision there is a greater risk during the learning curve of piriformis tendon injury and cup malposition.
    The Microport reamers are extremely sharp which means it is essential to ream centrally within the acetabulum. Because of the tight exposure, the Greater trochanter has a tendency to deviate the thin reamer stalk and can cause unintentional reaming of the superolateral wall.
    I tend to start the first reamer relatively vertically or open to ensure that I have reamed medially and have cover under the superior acetabular rim.

    Once I am happy that I am at the correct depth, I peripherally expand usually using odd numbered reamers advancing in 2mm increments until I feel I am approaching optimum cup diameter . As I increase in size, I am able to direct the reamer in the preferred 40/20 position for closure and anteversion.

    The angled reamer shell holder allows easy insertion and extraction of the reamer shells; the slim reamer stalk is easily located in the shell once it is located in the acetabulum.

    A 40/20 reaming position is facilitated by the thin reamer stalk. It is essential that care is taken to ream the acetabulum concentrically.
    After each episode of reaming the quality and integrity of the acetabulun should be reassessed; overreaming should be avoided

    For a Microport Procotyl Cup, line to line reaming is preferred- ie the last reamer diameter matches the nominal diameter of the shell.
    The cup adapter is screwed into the shell. This allows controlled shell impaction without direct linkage of the impactor to the shell which is desirable in a tight exposure.

    The stalk is only loosely attatched to the adapter screw so be careful not to drop the cup !
    There are fixation screw holes in the cup and these should be orientated towards the superior acetabulum if extra fixation is required.

    Once the cup is inserted, a check needs to be made of orientation and depth.
    The closure of the cup is usually 40 degrees.
    The anteversion is usually 20 degrees but heed should be taken of the degree of femoral anterversion. If the femur is retroverted, the cup should be a little further anteverted; the combined anterversion should not exceed 45 degrees.
    If all correct the liner can be inserted and any osteophytes removed at this stage.

    Both ceramic and HXLPE liners are available ; I generally use a lipped 32 mm XLPE liner, positioning the lip posteriorly.
    Below 50mm shell diameter, a 28mm liner is required.

    The Microport Procotyl system has Ceramic and Highly Crosslinked liners.

    The Microport femoral trials have a modular neck for ease of exposure and there is a comprehensive inventory of trial offsets and neck lengths which may be predicted during preoperative templating.
    The trial neck is inserted into the femoral trial stem using bespoke instrument holders. It is advisable to lavage the femoral component to facilitate neck insertion. The neck is then tapped into place using an angled impactor.

    Trial head components with differing lengths are available. The selected head is impacted using the angled impactor and the hip is reduced by pushing distally with the impactor with the assistant pulling and slightly adducting the leg.

    In the absence of intraoperative imaging, leg length can be assessed by palpating the knees with both hips in 20 degrees of flexion. Unlike anterolateral or posterior approaches, the length can also be assessed with Schuck type test to determine longitudinal joint laxity. Division of the superior capsule alone should not increase joint laxity and therefore, an appreciation of joint tension at trial reduction is a good indicator of leg length.

    The trial component is removed and the selected cementless Profemur stem is then impacted.

    The stem is impacted until its shoulder is snug with the femoral neck cut. A final measurement with the feeler guage can be performed measuring the length relative to the Greater Trochanter; if there is any uncertainty, a further reduction can be made with a trial head. When satisfied, the definitive head is impacted with the angled impactor and reduction effected.

    Once the retractors are removed the wound practically closes itself .
    A deep retractor is place to retract Gluteus medius and Piriformis and a PDS suture can be used to close the longitudinal incision in the superior capsule. The retractor is withdrawn and a looped PDS can then be used to close the interval between Medius and Piriformis. The fascia over gluteus maximus is closed. Fat suture with Vicryl, PDS subcuticular, skin staples and dressing.

    This is not intentionally small incision surgery but it is not necessary to use a large incision.
    The object of surgery is to preserve the hip capsule.

    Pre-operative templating of the left Hip for the implant

    Operation – 3

    The post operative X-ray.

    Post Operative

    Assuming the patient has had an appropriate anaesthetic ( light GA followed by half dose spinal), the patient is able to painfree straight leg raise and abduct in the Recovery Suite.
    If this is the cas, I ask the patient to sit on the side of the bed and then mobilise for a few steps with a Zimmer Frame. The patient is taken to the xray department and subsequently mobilised by physiotherapists.
    The levels of discomfort compared with a conventional approach are remarkably low and in appropriate circumstances, it is possible to send patients home on the day of surgery and certainly within 24 hours.

    Recommended Reading

    Reference

    • orthoracle.com

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