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Unicompartmental Knee replacement- Journey Uni (Fixed Bearing) Smith and Nephew

    Overview

    Learn the Unicompartmental Knee replacement: Journey Uni (Fixed Bearing) Smith and Nephew surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Unicompartmental Knee replacement: Journey Uni (Fixed Bearing) Smith and Nephew surgical procedure.

    This technique details the use of a Smith & Nephew Journey unicompartmental knee replacement (UKR) for a 63 year old man with knee pain secondary to medial femoral condyle avascular necrosis.
    History, examination and investigations were consistent with localised medial knee pain and a failure of conservative treatment. With sparing of the patellofemoral and lateral compartments the decision was to proceed to UKR. It was established prior to surgery that the patient’s cruciate ligaments were intact and functional. Pre-operative counselling and consent included a potential change to total knee replacement on table if on further inspection of the joint on arthrotomy more widespread disease was present. There is however strong evidence that some patellofemoral wear, especially affecting the medial facet of the patella, does not adversely affect the outcome of medial unicompartmental knee replacement.
    The Smith & Nephew Journey is a fixed bearing unicompartmental knee replacement manufactured with advanced bearing materials. Fixed bearing designs have seen increasing popularity in recent years according to the National Joint Registry (UK). This Journey design benefits also from simplified instrumentation which can aid the technique in what is a less frequently performed procedure than total knee replacement.


    Indications

    Indications include:
    Primary or secondary osteoarthritis limited to a single compartment
    Contraindications include:
    Active infection
    Significant and symptomatic osteoarthritis affecting other compartments
    Inflammatory arthropathy
    Fixed flexion deformity (as unable to correct intraoperatively)
    fixed significant varus deformity
    Absent ACL (unless performing simultaneous ACL reconstruction)
    Inadequate bone stock
    It is vital that the patient is consented for a potential on-table change to a total knee replacement if more widespread osteoarthritis is discovered at the time of arthrotomy.
    SYMPTOMS & ASSESSMENT:
    The patient’s overriding symptom was pain affecting the medial side of the knee only. Even stair climbing was relatively spared. The symptoms coincided with the development of avascular necrosis and plateau’d when indeed the MRI finding demonstrated that the disease had burnt out. Although the patient developed a varus deformity on standing this was fully correctible.
    INVESTIGATION:
    Both MRI and weight-bearing x-rays, including skyline views, were used to assess the degree of damage to the knee and to follow the course of the avascular episode. Although not common in my practice but some surgeons prefer to perform an investigatory arthroscopy to assess the extent of damage to articular surfaces in order to plan the appropriate arthroplasty surgery. This can be of particular benefit if there is doubt of inflammatory arthropathy or a history of joint infection, where synovial biopsies can be taken.
    OPERATIVE ALTERNATIVES:
    Total knee replacement
    High tibial osteotomy
    NON-OPERATIVE ALTERNATIVES:
    Continued conservative options include pain-relief, physiotherapy and off-loading knee brace.

    Setup

    A high thigh tourniquet is applied. Pre-operative antibiotics are given in line with the hospital’s formulary taking into consideration any patient allergies. The operative field is shaved of hair. A side support, L-shaped foot bracket and sand bag is used to support the knee in a flexed position of around 90 degrees. The surgeon can choose whether to stand on the same or opposite side to optimise ergonomic comfort and visualisation.

    Operation – 1

    The patella, tibial tuberosity, joint line and planned incision (dotted line) are marked out
    Commence with the knee at around 90 degrees and by identifying the tibial tubercle, medial edge of the patella and medial joint line. For the purposes of demonstration the patella, tibial tuberosity and medial joint-line have been drawn in the images. The dotted line is the planned surgical incision and measures 10cm in total.

    Set up includes a high thigh tourniquet, side support, footplate and sandbagThe tourniquet should be high enough so as not to interfere with the operative field and not restrict deep flexion.

    The skin incision is made commencing adjacent to the medial edge of the patella and running distally, parallel to the medial edge of the patella tendon to the medial 1/3 of the tibial tuberosityExtending the incision at the proximal end is often necessary once the arthrotomy is made to allow good visualisation of the superior edge of the medial femoral condyle. In this case proximal extension can be performed in line with the original incision.

    Expose the medial retinaculum and perform an arthrotomy as per a limited parapatellar approachAny medial release of the capsule and deep medial structures should be restricted to the proximal 6-8mm of the tibia to improve exposure and avoid releasing or stretching the medial collateral ligament. It is imperative to not overrelease as this could shift the weightbearing access onto the lateral side of the knee rather than through the prosthesis as planned. Progression of lateral compartment OA could lead to failure and reoperation. The release is performed to allow extraction of the cut tibia (see below).

    Excise any medial femoral osteophytes from the medial border and the notch with a sharp osteotome

    Inspect the patello-femoral and lateral compartments of the knee and confirm the integrity of the anterior cruciate ligamentThis is best achieved in extension to slacken the extensor mechanism, thus optimising the view of the patellofemoral and lateral compartments. Care must be take to avoid inadvertent damage to the articular cartilage with retractors.
    The ACL must be intact and functional. Some articular damage to the patella, particularly the medial facet is allowed and some authors even report full-thickness. However the surgeon should be more circumspect with any macroscopic changes in the lateral compartment. In my practice visible wear in the lateral compartment would lead to me abandoning the UKR in preference for a total knee replacement.
    At this stage the final decision is made to proceed to unicompartmental replacement or a change to a total knee replacement.

    The tibial jig is set up on the back tableThis technique utilises the spacer-block method of extension gap balancing. Therefore the first bony cut is the tibial resection. The tibial resection jig is assembled on the back table. The cutting block has a neutral slope so desired posterior slope is adjusted by releasing the gold clamp (A) and sliding the boom (B).
    The aim of the posterior slope is to increase femoral rollback and thereby improve flexion.

    The tibial jig is applied using a clamp around the ankle and slope adjusted as desiredThe vertical boom should overlie the medial third of the tibial tubercle and run parallel to the anterior edge of the tibia. By centralising on the ankle (between the medial and lateral malleoli) and the tibial tubercle coronal deformity of the tibial shaft can be discounted. Height can be set by using a stylus (A). For this particular system this comes set at 2mm, 4mm, 6mm and 8mm. My preference is to set 6mm resection to avoid overstuffing the medial compartment later. I find that despite a generous tibial cut the insert will often downsize on trial to avoid flexion and extension tightness. The tip of the stylus must sit on the worn tibial plateau (typically anterior 1/3 of the surface for isolated medial compartment OA with an intact ACL).
    Fix the height of the cutting block at this stage by tightening the screw (B).

    Medio-lateral positioning of the cutting block can be adjusted and fixed by tightening the screw in the block using a hex head driverIt is vital to ensure that:
    a) the block is set such that the vertical cut skims the medial edge of the ACL tibial insertion, on the medial downslope of the medial tibial eminence to maximise the size of the tibial base and avoid medial overhang,
    b) the block is not INTERNAL ROTATED – the patellar tendon has a tendency to push the block if not adequately retracted. Use the lateral wall of the medial femoral condyle as a guide for AP direction.
    The block is fixed using the headed intersection pin at the base of the vertical cutting slot. This pin acts to not only control rotation but also to limit the depth of the sagittal cut.
    Finally headed pins fix the block at the desired height. The planned cut is checked with an angel wing.

    A reciprocating saw is used to make the vertical sagittal cut skimming the medial edge of the ACL anteriorly and parallel to the lateral wall of the medial femoral condyleMost of the medial tibial eminence is included in the cut. The depth of the cut is limited by the intersection screw. Care must be taken to ensure the cut is complete posteriorly.

    Next the transverse cut is completed using an oscillating sawThe medial collateral ligament is protected with a retractor. This is a “blind” cut posteriorly so care must be taken when approaching and cutting through the posterior cortex. Some surgeons may prefer to stop short of the posterior cortex and complete the cut with an osteotome under direct vision. Although the neurovascular bundle is usually central or lateral to the centrepoint one must be aware of the excursion of the oscillating blade.

    Remove the tibial cutAny sharp dissection of soft tissue attachment should be under direct vision.The excised cut fragment can be used to give a rough guide as the size of the tibial tray.

    The flexion and extension gap is checked with the use of the gap stickThis is inserted with minimal resistance. The gap stick comes in 1mm increments from 7mm to 11mm. In my experience I aim for a minimum of 8mm as this allows for leeway to downsize the thickness of the tibial trial later. The gap stick can also be used to check varus/valgus alignment with a rod.

    The distal femoral cut is made next, based off the tibial cut to ensure a square and balanced extension gapBased on the thickness of the gap stick from the previous step (slide 13) the corresponding trial tibial insert to attached to underside of the distal cutting block, in this case a 9mm trial.

    The assembled distal cutting block is inserted and the leg is brought into full extensionThe block is pinned with headed pins. An alignment guide, using a separate jig and rods which attach to the block, can be added at this stage to check long-leg alignment before committing to the distal femoral cut.

    The distal femoral cut is made using the oscillating sawThis is fairly nerve-wracking! It is imperative to protect the medial collateral ligament with a retractor. Also cutting towards the back of the knee in extension must be performed with caution, especially as the view is obscured by the block. It is often advisable to perform as incomplete cut of around 90% of the depth, removed the block and complete the cut with a saw under direct vision, using the cut as a guide or rasp any remnant posterior bone.

    The thick end of the gap stick is now used to check the extension gap for stability and alignmentTest the tension in the medial collateral ligament with a values strain

    The knee is flexed to 90 degrees to expose the cut surface of the distal femur in order to size the femoral componentIt is imperative to have a good view of the anterior as well as the medial and lateral edges of the cut surface for accurate sizing. The cutting block is applied flush against the cut surface and the posterior condyle. The blocks “grow” anteriorly with increasing size. The correct size covers the largest surface without overhang. The block is pinned in place.

    Two peg holes are drilled through the cutting blockA peg is inserted into the anterior peg hole to stabilise the block prior to cutting the posterior and chamfer saw cuts.

    Posterior condyle cut is madeCaution as ever must be taken to avoid damage to the MCL during the posterior saw cut or damage to the tibial surface during the chamfer cut. After the cuts are complete the cutting block is removed.

    Tibial surface sizing using the templatesThis is the best stage to assess the size of the tibial surface using the sizing block (A). This system has a hook sizer (B) that can be clipped into the tibial sizing block to catch on the posterior edge of the cut surface.

    The tibial sizing block with the best tibial surface coverage is selectedIt is important to ensure that the block is flush with the vertical cut in the lateral edge of the tibial cut surface and not overhanging medially. Significant implant overhang can lead to MCL / medial capsular irritation and pain. If there is good AP coverage but greater than 2mm medial overhang you have to question if the vertical tibial cut is sufficiently lateralised.

    Insertion of the correctly sized tibial tray is done freehandOnce sized the appropriate tibial trial is inserted, again ensuring that the tray is flush with the vertical cut.

    The femoral trial and insert are insertedThe size of the insert will usually coincide with the depth of the gap stick used to test the flexion/extension gap (slide 17). However this is the opportunity to take time to trial with different depth inserts until optimal balance is achieved. Avoid an insert that overstuffs the medial compartment. As a general rule the insert should be easy to insert and allow up to 2mm opening on valgus stressing.

    Posterior capsule is infiltrated with local anaestheticOptional step: on removing the trial inserts I perform a posterior capsular local anaesthetic infiltration with 0.2% ropivacaine. Discuss this option with the anaesthetist beforehand.
    The cut surfaces are cleaned of blood, fat and debris with pulsatile lavage. Definitive implants are checked and taken in prior to mixing cement. Optimal exposure is ensured to allow implantation in the order: 1) tibial tray 2) femoral implant 3) tibial insert (or trial for cementation).

    Operation – 2

    The definitive implants are cementedMy preference is to use the trial tibial insert whilst the cement is curing. This is then removed and allows a good view to remove any remaining cement at the back of the knee and a final washout.

    The definitive insert is implanted and checked for correct seatingAny remaining exposed cement is removed.
    All retractors are removed and the knee is cycled to ensure a smooth balanced movement and ideal patellar tracking. Final washout is performed.

    The wound is thoroughly irrigated with normal saline using pulse lavage and closed in layersCapsule and fascia – absorbable suture (tip: when closing the extensor mechanism proximally complete and lock the suture on the quads tendon. If there are any muscle sutures these should be interrupted sutures. A continuous suture starting or finishing in muscle could cause death and atrophy to the ligated muscle and subsequent dehiscence of the entire layer.) Special attention should also be made to ensuring watertight closure of the distal end of the deep layer. This prevents the haematoma leaking from the “bottom end” and so avoids creating a sinus from skin to the prosthesis.

    Subcutaneous layer closure with absorbable sutureThe iodine-based dressing can be carefully lifted at this stage to ensure that there is no inadvertent button-holing in the skin.

    Skin – clips ensuring that the skin edges are evertedThe soft tissues should be respected at all times. I prefer to use finer forceps for closure. The wound is again irrigated. No drains are used.

    The wound is thoroughly cleaned and dried before applying a waterproof dressing, wool and crepeThe tourniquet is released. Distal pulses and capillary refill are checked before the patient is allowed to leave the operating theatre.

    This is the AP weight-bearing image demonstrating avascular necrosis of the medial femoral condyle and subsequent failure of the medial compartment.

    Post-op AP view

    Post-op lateral view

    Post Operative

    The wool and crepe dressing is taken down after 24 hours but the waterproof dressing should be maintained for 14 days so long as it is not too wet or the seal is broken. Skin clips are removed at 14 days.
    The patient commences supervised physiotherapy as soon as comfortable and mobilised full weight bearing once safe. Ideally a flexion angle of 90 degrees should be achieved prior to discharge. It is unusual for unicompartmental knee replacement patients not to achieve this within 3-4 days.
    AP and lateral radiographs are taken as an inpatient. Routine bloods tests are checked. Anticoagulation should follow local protocols and should include mechanical and chemical prophylaxis.
    Outpatient follow-up usually arranged 6 weeks post-op but the patient must be reassured to contact the department should they experience any problems.
    Wound leakage – the wound should be dry after 3-4 days post-operatively. If not then the wound must be inspected as cleanly as possible. If the leak is slowing and expected to stop imminently then prophylactic oral antibiotics and re-assessment of the anti-coagulation medication should be considered. However the surgeon should have a low threshold for return to theatre and formal closure of the wound to avoid the risk of deep infection.
    Stiffness – post-UKR stiffness is rarer than in total knee replacement. The surgeon must take into account the patient’s pre-operative range of movement. Significant stiffness at the 6 week follow up period must be taken seriously. In my practice I communicate closely with the physiotherapy department to gain a picture of progress. The patient may very well benefit from increased supervision and hydrotherapy. If stiffness continues to 10-12 weeks a manipulation under anaesthetic is strongly advised.

    Recommended Reading

    It is interesting to note that the according to the National Joint Registry’s 2017 report the recorded use of fixed bearing insert prostheses has grown since the registry’s inception in 2003 against the mobile-bearing prostheses (In 2003 fixed-bearing vs mobile bearing: 17.5% vs 81.25%; in 2017 fixed vs mobile: 44.6% vs 55.4%).
    Revision rates amongst UKRs remains relatively high compared to primary total knee replacements. Many reasons for this have been postulated. There is a perception that revising a UKR is a simpler procedure than revision of a total knee replacement, which may lower a surgeon’s threshold to proceed. It should be appreciated however that the patient reported outcomes (PROMs) for revised UKRs, including those revised to a primary total knee prosthesis, mirror the PROMs of full revision TKRs. While this fact should not prevent a surgeon from revising a failing UKR it should influence their original decision about using a UKR as a “stop gap” procedure in younger patients.
    The “bottom line” figure for 10 year survivorship of a UKR for a 65-year old patient is 90% (or a 1% failure per year.) This compares to around 95-97% for a total knee replacement. The probability of revision for a 55 year old and younger male and female with a UKR is in the order of 18-19% at ten years which compares to 8-9% for total knee replacement. There is no significant variability across genders. A surgeon’s reluctance to perform arthroplasty in younger patients is understandable when taking into account these comparable data.
    Complication rates and mortality rates favour UKR over TKR. Furthermore the improved, or more physiological, function attained due to sparing of the cruciate ligaments leads to higher early PROMs results.
    Careful patient selection and good surgical execution with the surgeon’s preferred implant can lead to excellent results from unicompartmental knee replacement. Furthermore careful follow-up and auditing of results can improve vigilance especially for failing knees. A paper produced with reference to the New Zealand Joint Registry, which collects Oxford Knee Scores as part of the audit, demonstrated a strong correlation between low 6-month Kalairajah and early (>2 year) revision for UKR.

    National Joint Registry for England and Wales. 14th Annual Report. http://www.njrreports.org.uk
    14th Annual Report is available to download. The revision rates of fixed and mobile bearing UKRs is shown on page 121 (Fig 3.19 (c)).

    Survival and functional outcome after revision of a unicompartmental to a total knee replacement: the New Zealand National Joint Registry.Pearse AJ, Hooper GJ, Rothwell A, Frampton C.J Bone Joint Surg Br. 2010 Apr;92(4):508-12
    Analysis of the revision rates and PROM scores of patients who had undergone revision of UKR to total knee replacement should significantly poorer results that patients with primary TKR. This suggested that the practice of using a UKR as a “stop-gap” procedure in younger patients was ill-advised.

    Patient-reported outcomes after total and unicompartmental knee arthroplasty: a study of 14,076 matched patients from the National Joint Registry for England and Wales. Liddle AD, Pandit H, Judge A, Murray DW. Bone Joint J. 2015 Jun;97-B(6):793-801.
    Early (6-month) Oxford knee score was higher for unicompartmental knee replacement over total knee replacement. This paper also found that overall complications and re-admission rates were lower for UKR.
    Analysis of the revision rates and PROM scores of patients who had undergone revision of UKR to total knee replacement should significantly poorer results that patients with primary TKR. This suggested that the practice of using a UKR as a “stop-gap” procedure in younger patients was ill-advised.

    Patient-reported outcomes after total and unicompartmental knee arthroplasty: a study of 14,076 matched patients from the National Joint Registry for England and Wales. Liddle AD, Pandit H, Judge A, Murray DW. Bone Joint J. 2015 Jun;97-B(6):793-801.
    Early (6-month) Oxford knee score was higher for unicompartmental knee replacement over total knee replacement. This paper also found that overall complications and re-admission rates were lower for UKR.

    An analysis of the Oxford hip and knee scores and their relationship to early joint revision in the New Zealand Joint Registry A. G. Rothwell, G. J. Hooper, A. Hobbs, C. M. Frampton. J Bone Joint Surg [Br] 2010;92-B:413-18.
    Whilst demonstrating that low Oxford hip and knee scores at 6-months correlated well with early revision this paper’s strongest demonstration of a relationship was with a Kalairajah score of <27 (poor) being associated with a 27% risk of UKR revision within 6-months.

    Fixed- versus mobile-bearing UKA: a systematic review and meta-analysis. Peersman G, Stuyts B, Vandenlangenbergh T, Cartier P, Fennema P.Knee Surg Sports Traumatol Arthrosc. 2015 Nov;23(11):3296-305.
    Meta-analysis of 9463 knees (44 papers) showed comparable revision rates for fixed bearing UKR and mobile bearing UKR, 0.9 and 1.51 per 100 component years respectively.

    Reference

    • orthoracle.com

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