RECONSTRUCTION 2023, Jan, 08 | 12:00 am

Unicompartmental Knee Arthroplasty

P ITFALLS

  • Heavy, active patients.

  • Be careful if the ACL is compromised. ACL deficiency is a relative contraindication, but this may be implant dependent.

     

  • Significant angular deformity or bone loss.

     

  • In osteonecrosis, magnetic resonance imaging is mandatory to rule out involvement of the other compartments.

     

  • Pain in the patellofemoral joint, even without obvious radiographic findings, should be seriously considered to be a contraindication.

     

  • Unlike total knee arthroplasty (TKA), a stiff and/or significantly imbalanced knee cannot be adequately corrected with unicompartmental knee arthroplasty (UKA).

     

  • Inflammatory arthritis, especially rheumatoid arthritis, is a contraindication.

 

Unicompartmental Knee Arthroplasty

 

Indications

  • Unicompartmental disease.

  • Thin and/or less active patients.

  • Women are often favored.

  • Bimodal age distribution. Appropriate for younger, low-demand patients wishing to postpone total knee replacement. Also appropriate for older patients seeking less invasive option than total knee replacement.

  • Varus angulation less than 12°.

  • Flexion contracture less than 15°.

  • Ligamentous stability and competence (anterior cruciate ligament [ACL] competence may be relative).

  • Good bone stock.

  • Minimal patellofemoral disease. Significant patellofemoral pain is considered a contraindication.

    Examination/Imaging

  • Routine physical examination focusing on stability, range of motion, and muscle and skin integrity is mandatory. Physical findings of significant synovitis should prompt an evaluation for inflammatory arthropathy.

  • Patellofemoral joint tenderness, compression pain, crepitus, maltracking, or obvious anterior compartment pain should preclude UKA. Pain in

    the lateral compartment should also preclude UKA.

  • Severe angular malalignment and flexion contracture make unicondylar knee replacement technically difficult.

    Controversies

    • There is little disagreement that the medial collateral ligament (MCL), lateral collateral ligament, and posterior cruciate ligament (PCL) must be functional to have a well-functioning UKA.

    • ACL stability has historically been considered mandatory for UKA. With the advent of more conforming designs, there is more emphasis on overall knee stability than on the ACL itself. Unicondylar replacement has been combined successfully with ACL reconstruction.

     

  • Plain radiographic evaluation to include anteroposterior (AP), lateral, posteroanterior (PA) flexed, and patellofemoral (sunrise) views is mandatory.

    • In Figure 1, standing AP (Fig. 1A), PA (flexed), lateral (Fig. 1B), and sunrise (Fig. 1C) views demonstrate unicompartmental disease.

    • The flexed view will allow a better evaluation of the posterior aspect of the knee and may reveal more significant changes in the posterolateral compartment.

    • Full-length standing radiographs from the hip to the knee are very helpful, particularly if computer navigation techniques are used.

       

      • Obesity, high activity level, and younger age groups have historically been linked to early failure. With improvements in knee design and implant technology, these relative contraindications are being reassessed.

      • As with high tibial osteotomy (HTO), arthroscopic evaluation has not been an effective predictor of patellofemoral response to UKA.

       

       

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      Treatment Options

      • Alternatives to UKA include those treatments similarly limited to unicompartmental disease.

      • Conservative options include unloading braces. These should probably be reserved for early disease, high activity level, and male patients in whom weight-bearing valgus stress on exam provides relief.

      • HTO, whether by dome, medial opening, or lateral closing wedges, can be considered in patients similar to those for whom UKA is indicated.

        • HTO seems to be less acceptable to women, particularly those whose thighs may rub after overcorrection of the deformity.

        • HTO is more accepted in men, particularly those who are young, with high activity levels.

       

      Unicompartmental Knee Arthroplasty

       

      A

       

       

       

      B

       

       

       

      C

      FIGURE 1

       

  • Preoperative templating can be done for UKA. In Figure 2, note the position of the components on femoral AP (Fig. 2A) and lateral (Fig. 2B) views, and bone resection on the tibia (Fig. 2C).

     

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    7.0mm

    Size 3

     

     

     

     

     

     

    Unicompartmental Knee Arthroplasty

     

    Joint line

     

     

    FIGURE 2

    A B C

     

    Surgical Anatomy

    • Patellar tendon

    • MCL

    • Medial meniscocapsular ligament

       

      P EARLS

      • Place a buttress on the side of the thigh so that a valgus force can be applied as one would do during arthroscopy.

         

      • Place a sandbag that will hold the leg in a variety of positions, including “figure-4” position.

         

      • If computer navigation is to be used, maximize access to the thigh and calf for placement of trackers and to the malleoli for identification of landmarks.

       

    • ACL

    • PCL

      Positioning

    • Positioning for the procedure should mimic that of a TKA.

    • Particularly with minimally invasive procedures, it is important to position the leg so that dynamic retraction methods can be combined with a variety of leg positions.

    • One must be prepared to convert the procedure to TKA.

    • Supine positioning with a sandbag just distal to the knee or a foot/leg holder that allows flexion-extension of the leg is helpful.

       

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      P ITFALLS

      • Do not limit the knee exposure in draping, as you may need to convert to TKA.

       

      Unicompartmental Knee Arthroplasty

       

      • A tourniquet should be used and placed as high on the thigh as possible.

      • If computer navigation is to be used, positioning should accommodate full circumduction of the hip.

        Portals/Exposures

        Controversies

        • Setting up as for an arthroscopy with the foot hanging is an option, but this may limit some ability to perform TKA if required.

         

      • To help ensure a rapid rehabilitation, techniques similar to those termed minimally invasive for TKA should be employed.

    • A longitudinal, medially based incision is utilized (Fig. 3A; see Video 1). The incision must be positioned to allow access to/visualization of the patellofemoral joint and the ability to convert to TKA. This is basically a slightly shorter (distal portion) version of the medially based incision used in minimally invasive TKA.

 

 

 

A B

 

 

 

C

FIGURE 3

 

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P EARLS

  • An incision just medial to the patellar tendon and slightly oblique toward the medial edge of the patella works well. Freeing up subcutaneous circumferential flaps will help mobilization throughout the case.

     

  • It is important to cut the meniscus to release the periosteal flap for medial dissection.

     

  • Perform a patellar facetectomy, especially if prominent patellar osteophytes interfere with exposure.

     

  • Perform a complete medial meniscocapsular ligament release from anterior to posterior. This aids in the removal of the tibial wafer after it is osteotomized.

     

  • Resect the medial side of the retropatellar fat pad.

     

    P ITFALLS

  • The incision should not be placed too far medially as it may limit conversion to TKA if required.

     

  • Protect the patellar tendon and MCL.

     

  • Remove all osteophytes interfering with exposure.

     

  • Avoid struggling with difficult exposure. Consider repositioning the leg, performing débridements after the relaxing effects of osteotomies, or simply extending the approach as needed.

     

  • Overcorrection through a medial release is clearly contraindicated. The current trend is generally to leave the limb alignment slightly undercorrected with mild pseudolaxity with valgus stress.

 

Unicompartmental Knee Arthroplasty

 

  • The arthrotomy is linear and parallels the fibers of the patellar tendon (Fig. 3B), extending down to the bone on the tibia and up to the inferior portion of the patella (see Video 1; this case required a small patelloplasty). Figure 3C represents a typical incision for the unicompartmental level.

    • The meniscus is incised to release the soft tissue from the tibia, and a subperiosteal flap is developed in a circumferential pattern posteromedially around the tibia (Fig. 4A–C).

  • Much as for a mildly arthritic primary TKA, this flap is extended posteriorly as a medial release and is carried as far posterior as necessary to allow ligamentous balance (see Video 3). Generally, release of the semimembranosus complex is not required.

  • The medial release can be extended subperiosteally to aid exposure and slight correction of deformity (Fig. 4D). In general, the goal is not to “correct” the preoperative alignment; slight pseudolaxity should be present with valgus stress at the conclusion of the procedure.

  • The postoperative scar is relatively cosmetic (Fig. 4E).

 

 

 

 

 

 

 

 

Unicompartmental Knee Arthroplasty

 

 

 

 

 

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B

 

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D

 

E

FIGURE 4

 

 

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Instrumentation

  • Downsized instruments are needed.

  • Bent retractors that gently displace tissues and keep the assistant’s hands out of the surgeon’s field of view are important.

  • Angled knee retractors are helpful medially. Laterally, a straight dull Hohmann retractor seems to more easily retract the patella.

  • Be cautious when flexing and extending the knee as the retractor can impinge on the patella cartilage or get compressed in the notch.

 

Unicompartmental Knee Arthroplasty

 

  • With use of retractors, and flexion/extension of the knee, the patellofemoral joint can be examined for damage that may preclude UKA (extend the knee to improve visualization of the patellofemoral joint).

  • At this point, the knee can be flexed and an angled retractor placed medially to protect the MCL (Fig. 5A and 5B). The medially based incision well exposes the medial side of the knee for implantation.

  • A dull, straight Hohmann retractor can be placed into the femoral notch and used to retract the patellar tendon (Fig. 5C). (Be careful to remove this retractor if the knee is brought to extension, to avoid risk of fracturing the tibial spine or damaging the trochlear cartilage.)

  • While the knee is extended, a tidemark of sorts can be marked to document the height of the anterior tibial-femoral articulation for later reference when confirming the anterior extension of the femoral component required for effective articulation with the tibia (Fig. 5D).

 

 

 

A B

 

 

 

C D

FIGURE 5

 

 

P EARLS

  • The medial edge of the tibial resection will be quite thin.

     

  • The tibia will be used for double checking during the rest of the procedure.

     

  • The tendency is to cut in varus; do not be fooled by the thinness of the bone medially.

 

Unicompartmental Knee Arthroplasty

 

Procedure

Step 1: Tibial Cut (see Video 4)

  • Most unicompartmental knee system instruments start with the tibial cut. This allows better visualization for the rest of the procedure and provides the ability to “match” the posterior femoral resection to the tibial resection for flexion balance. Extramedullary alignment jigs are used most commonly, although computer navigation is on the horizon.

  • The alignment rod should parallel the tibial shaft,

and the plateau resection should be perpendicular to this axis (Fig. 6A–C). Depth of cut and slope can be based on this alignment.

 

 

 

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A B

 

 

 

C FIGURE 6

 

 

 

 

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Unicompartmental Knee Arthroplasty

 

D E

FIGURE 6, cont’d

 

 

P ITFALLS

  • Do not cut the tibia in varus or valgus.

     

  • Fixation pins, particularly multiple and converging pins, create stress risers and may lead to late fracture.

     

  • Watch the cruciates when cutting the sagittal cut, and do not pass deeper than the

transverse cut and create a stress riser.

 

  • After the tibial cutting guide has been set, one can visualize the depth of cut. The medial aspect will be relatively thin compared to the lateral portion (Fig. 6D and 6E).

  • Do not cut in varus or valgus. This generally means that the medial edge of the tibial resection will be quite thin. If one were to err, erring to thinner and valgus is least problematic. Visually it can be deceptive: if it looks varus, it probably is.

    • Relative to slope, try to match that of the patient’s anatomy.

      Instrumentation/ Implantation

      • Use a very narrow oscillating saw.

       

  • A blade can be placed into the joint along the natural tibial slope, and the cutting guide positioned to match in parallel for re-creation of slope in the reconstruction (Fig. 7A). This technique provides a strong visual cue.

  • Figure 7B shows a preoperative radiograph of the natural tibial slope, and Figure 7C shows the postoperative re-creation of the natural tibial slope.

    Controversies

    • Inset components may subside and fail, particularly when in soft bone. While this technique is popular, the cortical rim is strong and preferred for support.

     

  • Err to increased slope, as the natural error is an undersloped cut. However, oversloped cuts should also be avoided. Figure 7D shows a postoperative example of overzealous correction and too much slope.

    • The removed tibial fragment will generally be thinner medially and posteriorly.

  • This cut should be rigorously inspected since it will be used to set the femoral cut block and locks in the rotation of the femoral component.

     

     

     

     

     

     

     

     

     

     

    Unicompartmental Knee Arthroplasty

     

     

     

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    A

     

    B

    FIGURE 7

     

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    D

     

     

     

     

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    Unicompartmental Knee Arthroplasty

     

    FIGURE 8

     

  • The resected fragment of tibia can be compared for size to the trial component (Fig. 8).

    • Spacer blocks should be placed into the joint and the stability/balance tested in flexion and extension. As noted, there should be slight pseudolaxity with valgus stress.

    • The tibial portion of the procedure can be the source of problems and lead to early and late failure of the construct.

  • Pins used for fixation of the cutting block can be the source of stress risers that lead to late fracture. In the postoperative radiograph in Figure 9A, note the pin tract just under the keel creating a stress riser.

  • Be careful not to use multiple or converging pins; they cause stress risers and risk fracture. The postoperative radiograph in Figure 9B shows multiple pin tracts just under the keel creating stress risers, leading to a postoperative fracture through the pin tracts (Fig. 9C). Figure 9D shows the bone loss resulting from the fracture.

  • The sagittal cut along the spine can similarly lead to fracture; be careful not to pass-point with the cut (Fig. 10A). Figure 10B shows a postoperative rupture of the PCL with resultant posterior sag, likely secondary to injury from the sagittal saw.

  • Components inset in soft bone may subside and fail. Generally, the cortical rim is strong and may be preferred for component support.

 

 

 

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Unicompartmental Knee Arthroplasty

 

A B C

 

 

Lateral plateau

 

Defect

 

 

D

FIGURE 9

 

 

 

A B

FIGURE 10

 

 

 

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Unicompartmental Knee Arthroplasty

 

FIGURE 11

 

 

 

P EARLS

  • Use the tibia to set the femur, and use its position relative to the femur to mark the center point.

     

  • Take away what you plan to put back on the distal femur.

     

  • Take time during the femoral preparation. Double-check everything prior to committing to final position and cutting the keel or drilling the peg.

     

  • Err to lateralization of the femoral component. It will end up where you wanted it.

     

    P ITFALLS

  • The tendency is to internally rotate the component; be careful.

     

  • A large component or extension too anterior may cause impingement on the patella.

     

  • Watch for edge loading from medialization or malrotation of the femur.

 

A B

 

  • Over-resection of the tibia may be somewhat unavoidable in relatively small knees, but care should be taken to be proportional. Figure 11A demonstrates over-resection of the tibia.

  • The cut posteriorly is a bit blind and some sagittal saws have teeth on both sides. Inadvertent laceration of the ACL or PCL can lead to late instability.

  • Over- or underslope, varus cuts (Fig. 11B), and valgus cuts all can lead to imbalance.

    Step 2: Femoral Cuts

    • The unicompartmental knee system instrument is now used for the femoral cuts.

  • With the tibial cut established, a block can be placed into the 90°-flexed knee and a measured resection made of the posterior condyle (see Video 5).

  • The knee system used for the reconstruction will determine how the distal cut is made and whether there are chamfer cuts. Video 6 shows an implant system that uses a routing preparation of the distal femur; other systems use more traditional saw cuts. In general, the amount of resection of the distal femur should match that which is replaced by metal.

  • The extent of cartilage wear will, in part, determine how the cutting jig is placed. Familiarity with the system is imperative. The jig may require total removal of the remaining medial femoral cartilage for proper measured resection. Alternatively, the system may base the resection from the areas with little to no wear. The issue is really what depth of cut is desired from the jig

     

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    Instrumentation/ Implantation

    • Know the instruments. Know if you are basing the distal cut from the bone base or the most normal cartilage point.

     

    Unicompartmental Knee Arthroplasty

     

    relative to the thickness of the implant. Again, the goal is to recreate the norm.

    • Once the cuts are made, most systems will cut a groove for a keel or drill a hole for a peg. In either case, this is the point of no return and commits the component to its final position.

      Controversies

      • The femoral component needs an augmented fixation keel or pegs for stability; the system and style are the surgeon’s preference.

       

      • Since the tibial preparation is complete, it is helpful to mark the center point of the tibia relatived to the width of the femoral condyle. The femoral

        component should be placed so it is center-point on the tibial polyethylene. Usually, this means the femoral component needs to be “cheated” a bit laterally. This is visually disturbing. If the component is placed on the femoral condyle in such a way that it covers the medial aspect, it will end up too medial and lead to edge loading in the final construct.

      • The femoral resection level and alignment are set from the tibial cut.

    • Figure 12A shows the femoral cutting guide placement. The jig is linked to a block that is based off the tibial cut.

 

 

 

A B

 

 

 

C D

FIGURE 12

 

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Unicompartmental Knee Arthroplasty

 

  • After posterior resection, a flexion block can be used to check stability and balance in flexion (Fig. 12B) and extension (Fig. 12C).

  • Extramedullary guides or navigation can be used to check rotation and femoral position (Fig. 12D).

    • The tibial cut should set the internal-external rotation of the femur. One should err to external rotation. The visual cues of the femoral anatomy tend to push toward nonanatomic internal rotation of the final components.

    • When choosing the size of the femoral component, the tidemark of the tibial-femoral articulation that was noted early in the case should be confirmed. The femoral component should extend to this height or very slightly past it.

  • If the component is too large and extends much past this point, it may impinge on the patella in flexion and cause pain or wear of the patellar cartilage. Figure 13A is a sunrise radiograph of a patient with anterior knee pain and femoral component patellar impingement.

 

 

 

A B

 

 

 

C FIGURE 13

 

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Unicompartmental Knee Arthroplasty

 

  • The intraoperative photo in Figure 13B demonstrates slight anterior flange recession to avoid patellar impingement. A slight patelloplasty can be performed to help decrease impingement (Fig. 13C).

    • Some systems require a slight undercut at this level so that the most anterior portion of the femoral component is slightly “recessed.”

    • Double-check the positioning of all the guides before cutting or routing the keel or drilling for the peg, since this is a “no turning back” point with respect to angulation/rotation.

    • The flexion stability should be confirmed prior to commitment to the final femoral cuts (Fig. 14A).

  • The post-resection photo in Figure 14B shows a balanced flexion gap, keel/peg preparation of the femur, and use of a dull Hohmann retractor for patellar retraction.

 

 

 

 

A B

 

 

 

C FIGURE 14

 

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Unicompartmental Knee Arthroplasty

 

  • Balance should be confirmed with trials and blocks (Fig. 14C).

    • Much of the femoral positioning is done freehand or eyeballed. Extramedullary guides, and in the future navigational guides, may lend support for this portion of the procedure.

    • The tibial portion of the procedure can also be a source of problems.

  • Ligamentous injury during any of the cuts will lead to late failure. Protect the ligaments with retractors and do not pass-point with the saw.

  • Malrotation of the femoral component, as in Figure 15A, may result in maltracking or edge loading. Failure to lateralize the femoral component on the condyle also can lead to edge loading on the tibial component (Fig. 15B). When templating, the position may appear “overly” lateral (Fig. 15C). Edge loading and/or femoral malrotation will lead to increased wear of the polyethylene.

     

    P EARLS

    • Place a sponge posteriorly around the tibia prior to cementing to help pull/clean out all the cement.

       

      P ITFALLS

    • Retained cement will be very problematic. Look for cement in the notch too.

     

    Step 3: Trialing and Cementation

    • Prior to cementing, a trial should be performed.

  • The knee should be stable through a full range of motion and there should be no patellar impingement.

  • Slight pseudolaxity with valgus stress is appropriate. It is generally accepted that the alignment of the knee should not be “fully” corrected. Overcorrection to valgus is clearly contraindicated as it can lead to lateral compartment wear and pain.

    • Standard vacuum mixing is appropriate. Only ½ bag is required.

      Controversies

      • Cemented components are the standard in the United States.

       

    • A sponge should be placed around the medial side of the tibia and posterior to the knee joint prior to cementing. When the components are in, the sponge can be pulled out and with it remnant cement.

    • Depending on the implant system, the tibia (see Video 7) or the femur (see Video 8) may be implanted first. Trial the real implants prior to implantation to be sure everything will fit.

    • While the cement cures, maintain extension to compress the components.

       

      Unicompartmental Knee Arthroplasty

       

       

       

       

       

       

       

       

      1mm

       

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      FIGURE 15

       

       

       

       

       

       

       

       

       

       

       

       

      Unicompartmental Knee Arthroplasty

       

       

       

       

       

       

       

       

       

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      A

       

      B

       

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      D

      FIGURE 16

       

      E

       

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      FIGURE 17

       

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      P EARLS

      • Outpatient physical therapy seems to be valuable as patients are treated with rapid rehabilitation much like those with athletic injuries.

         

        P ITFALLS

      • Work hard to control pain and swelling. The goal is rapid return to function.

       

      Unicompartmental Knee Arthroplasty

       

      Postoperative Care and Expected Outcomes

    • Figure 16 shows preoperative AP (Fig. 16A), lateral (Fig. 16B), and sunrise (Fig. 16C) views and postoperative AP (Fig. 16D) and lateral (Fig. 16E) views of a well-functioning UKA.

    • Postoperative care includes a focus on pain control to help facilitate early range of motion and rehabilitation.

    • As with TKA, deep venous thrombosis prophylaxis should be a part of postoperative care.

    • Early physical therapy with encouraged full range of motion should be pursued. Weight bearing should not be limited.

  • Video 9 depicts the gait of a patient 2 weeks after surgery.

  • Video 10 depicts a relatively early postoperative patient’s ability to squat.

  • Figure 17A and 17B shows postoperative flexion in two patients.

Evidence

Berger RA, Meneghini RM, Jacobs JJ, Sheinkop MB, Della Valle CJ, Rosenberg AG, Galante JO. Results of unicompartmental knee arthroplasty at a minimum of ten years of follow-up. J Bone Joint Surg Am. 2005;87:999-1006.

 

This was a minimum ten-year follow-up study of 62 cemented modular Miller-Galante unicompartmental knee implants. Surgery was performed in 51 patients who were then studied prospectively both clinically and radiographically. All patients had isolated unicompartmental disease and were without patellofemoral symptoms. After excluding the patients who died, 38 patients (49 knees) had a minimum ten-year follow-up (mean 12 years). The results showed very high Hospital for Special Surgery knee

scores, 80% excellent results and 12% good results. At final follow-up, no components were found to be loose radiographically or showed osteolysis. Twenty percent of the knees had radiographic joint space loss in the opposite compartment and 14% in the patellofemoral joint. This ten-year follow-up showed excellent clinical and radiographic results. The survival rate was excellent, although there were radiographic signs of osteoarthritic progression in the other compartments.

 

Bonutti PM, Seyler TM, Kester M, McMahon M, Mont MA. Minimally invasive revision total knee arthroplasty. Clin Orthop Relat Res. 2006;(446):69-75.

 

This report of 17 revision knee arthroplasties had average follow-up of 29 months. The focus of the report was an exposure technique for difficult total knees. A soft tissue envelope dissection technique allowed retraction of the patella and avoided patellar eversion. The size of the incision and quadriceps muscle damage were reported to be decreased. Exposure was reported to be enhanced. The preliminary results were very encouraging when using improved instrumentation of the enhanced exposure.

 

Collier MB, Eickmann TH, Sukezaki F, McAuley JP, Engh GA. Patient, implant, and alignment factors associated with revision of medial compartment unicondylar arthroplasty. J Arthroplasty 2006;21(6 Suppl 2):108-15.

 

This was a review of 245 fixed bearing unicondylar knee arthroplasties. Several different tibial implants were used during the study. Five factors were associated with revision. Younger patient age, thinner tibial component thickness, longer polyethylene shelf life, angular reduction of the medial plateau varus position and increased postoperative hip-knee-ankle angles. The deleterious effects of these factors were outlined and discussed in the manuscript.

 

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Unicompartmental Knee Arthroplasty

 

Deshmukh RV, Scott RD. Unicompartmental knee arthroplasty: long-term results. Clin Orthop Relat Res. 2001;(392):272-8.

 

This is a discussion of the long-term (10 year) results of unicompartmental knee arthroplasty. It outlines the progressions made in patient selection as well as surgical technique and those which lend themselves well to a better long-term outcome.

 

Hamilton WG, Collier MB, Tarabee E, McAuley JP, Engh CA Jr, Engh GA. Incidence and reasons for reoperation after minimally invasive unicompartmental knee arthroplasty. J Arthroplasty 2006;21(6 Suppl 2):98-107.

 

This is a report on an initial series of 221 unicompartmental knee arthroplasties that were performed using a minimally invasive technique. These cases were compared to a previous series of 514 medial unicompartmental knee arthroplasties that were performed in an “open” fashion. The authors found a higher rate of revision due to aseptic loosening, 3.7% for the minimal group versus 1.0% for the open group and the overall re-operation rate of 11.3% for the minimal group versus 8.6% for the open group. The re-operation and revision rates for a minimally invasive approach did not compare favorably to the traditional open method of unicompartmental knee arthroplasty.

 

Markel DC, Sutton K. Unicompartmental knee arthroplasty: troubleshooting implant positioning and technical failures [Review]. J Knee Surg. 2005;18:96-101.

 

This manuscript reviewed issues leading to failure of unicompartmental knee arthroplasties. Techniques to prevent failure and for improving longevity are outlined. In addition, the key technical points that seemed to lead to failure were described.

 

McAllister CM, Stepanian JS. Minimally invasive unicondylar knee replacment. In Hozack WJ, Krismer M, et al. (eds). Minimally Invasive Total Joint Arthroplasty. Heidelburg: Springer Verlag. 2004:172-80.

 

This chapter reviewed the techniques for performing a minimally invasive unicondylar knee arthroplasty. The chapter is included in a textbook which reviews techniques and philosophy regarding minimally invasive total joint arthroplasty as a whole.

 

McAuley JP, Engh GA, Ammeen DJ. Revision of failed unicompartmental knee arthroplasty. Clin Orthop Relat Res. 2001;(392):279-82.

 

This was a report of 39 consecutive unicompartmental knee revisions. The revisions were done with broad follow-up ranging from 9 to 204 months post index procedure. Polyethylene wear was the prominent mode of failure. However, 9 failed due to loosening. The revision procedures were felt to be relatively straightforward, although 10 patients required local autograft to augment the procedure. Interestingly, primary femoral components were used in all patients and 25 of these were cruciate retaining. On the other hand, 14 patients required stemmed tibial components, 8 of whom had wedge augmentation. While this series was relatively small, the outcomes and complications encountered with this revision surgery compared favorably with those of a total knee revision.

 

Murray DW, Goodfellow JW, O’Connor JJ. The Oxford medial unicompartmental arthroplasty: a ten-year survival study. J Bone Joint Surg Br. 1998;8:983-9.

 

This ten-year survivorship study reported on 143 knees. The knees had anterior medial osteoarthritis and reportedly normal anterior cruciate ligaments. The procedure employed a mobile bearing unicompartmental knee. Of the 109 living patients with mean follow-up of 7.6 years, outcome was quite positive. Worst case survivorship rate was 97%. No failures were noted due to polyethylene wear or aseptic loosening of the tibial component. The overall 10-year survivorship rate was “the best” of those reported for all unicompartmental knee arthroplasty procedures. It was not felt that these rates were significantly different from the “best” rates for a total knee arthroplasty.

 

Pagnano MW, Clarke HD, Jacofsky DJ, Amendola A, Repicci JA. Surgical treatment of the middle-aged patient with arthritic knees. Instr Course Lect. 2005;54:251-9.

 

This instructional course lecture reviews surgical treatment for middle-aged patients. It includes the gambit of nonsurgical and surgical options and discusses the application of both unicompartmental and total knee arthroplasty of this age sector of patients. It is an excellent resource as a baseline for treatment of the middle-aged patient with arthritis.