Unicompartmental Knee Arthroplasty
N.P. Kort, MD, PhD
Nanne P. Kort, MD
Mobile-bearing unicompartmental knee arthroplasty has become a viable treatment alternative for osteoarthritis that is confined to the medial part of the knee. Improved surgical technique and component design have led to increased popularity.With the introduction of the minimally invasive option, the terms learning curve and pitfalls become current again. Minimally-invasive mobile-bearing unicompartmental knee arthroplasty is technically demanding, and complications occur with placement of this unicompartmental knee device. This review presents the possible pitfalls, and provides tips and tricks for improving the outcome of mobile-bearing unicompartmental knee arthroplasty.
Mobile-bearing unicompartmental knee arthroplasty is an established treatment for the management of medial compartment osteoarthritis.1, 2It is gaining prominence as a standard reconstructive option in Europe and the United States.3
The Oxford phase-1 mobile-bearing unicompartmental knee replacement was first introduced in 1978, and was designed to allow large areas of contact between the femoral and tibial components, reducing the wear rate.13, 14Phase 2, introduced in 1985, had the significant improvement that the femur could now be prepared with a guided power mill instead of a saw, making precise ligament balancing easier.15In 1998, the 10-year survival analysis of the Oxford mobile-bearing unicompartmental knee replacement was published by Murray et al.1They claimed a 97.7% cumulative survival rate. The independent series with a 15-year survival analysis claims a 94% cumulative survival rate.16
In 1998 the phase-3 implant was introduced, partly to address the problem of inconsistent results by making the operation simpler as well as to facilitate a minimally invasive approach15The operation is now performed through a short incision from the medial pole of the patella to the tibial tuberosity (Fig 1). There is minimal damage to the extensor mechanism, the patella is not dislocated and the suprapatellar synovial pouch remains intact. As a result, patients recover more quickly. Knee flexion, straight leg-raising and independent stair-climbing are achieved three times faster than after TKR, and twice faster than after open unicompartmental knee replacement.17It is shown that the minimally invasive procedure is reliable and effective.18With appropriate pain control measures, the procedure can safely be done on an outpatient basis with substantial cost savings, and patients report less pain postoperatively than preoperatively.4
For a mobile-bearing unicompartmental knee arthroplasty, the osteoarthritis should be confined to the medial compartment.19It is not uncommon for patients who have anteromedial unicompartmental osteoarthritis to have isolated changes in one of the other two compartments, but minor changes in the other compartments do not seem to affect the results of a unicompartmental arthroplasty.19, 20
Not only anteromedial osteoarthritis but also avascular necrosis seems to be an appropriate indication for a mobile-bearing unicompartmental knee arthroplasty.15, 21It should be noted that the number of patients with this indication is very limited. Osseous bone loss should be evaluated to determine if there is enough bone stock for adequate fixation of the femoral component.
The typical osteoarthritis for a mobile-bearing unicompartmental arthroplasty is confined to the anteromedial compartment; the posterior parts of the medial tibial and femoral articular surface remain relatively intact, so that in flexion the medial collateral ligament is under normal physiological tension. Anteromedial osteoarthritis is also referred to as an extension gap disease. In case of rupture of the anterior cruciate ligament, the contact point in extension moves posteriorly, causing damage to the more posterior cartilage. The resulting loss of joint space in flexion allows the medial collateral ligament to remain shortened throughout the full range of movement of the knee, causing a contracture of the medial collateral ligament.22, 23Absence of the anterior cruciate is therefore a contraindication, because presence of the anterior cruciate ligament makes the combined rolling and sliding at the meniscal femoral and meniscal tibial interfaces possible, which may yield near normal joint kinematics and mechanics.24In correlation with above, the intra-articular varus deformity should be correctable, indicating that the medial collateral ligament is not shortened. Medial or lateral subluxation or posterior tibial bone loss strongly suggest damage to the cruciate ligaments and is therefore a contraindication for this procedure.
Flexion deformity should be less than 15 degrees. Mobile-bearing unicompartmental knee arthroplasty has only a limited ability to improve flexion deformity. The knee must be able to flex to at least 110% under anaesthesia, to allow access for preparation of the femoral condyle.25
Patellofemoral osteoarthritis is not a contraindication.1There is no influence on the clinical outcome, no progression is seen after a mobile-bearing unicompartmental knee arthroplasty, and patellofemoral osteoarthritis has not been a reason for revision,15although it may be a contraindication when patellofemoral symptoms are present preoperatively.26, 27
Patients with inflammatory diseases such as rheumatoid arthritis are not candidates for mobile-bearing unicompartmental knee arthroplasty because of synovial involvement of the opposite compartment.28, 29Knee arthroplasty in rheumatoid arthritis is associated with progression of RA and loosening of the components.30
The presence of chondrocalcinosis is not considered to be a contraindication for this procedure. There is no significant difference between survival rates of mobile-bearing unicompartmental knee arthroplasty groups with or without chondrocalcinosis.31Some studies suggest that any degree of obesity has a negative effect on the outcome of total knee arthroplasty. To date, there few studies on the outcome of unicompartmental knee arthroplasties in obese patients. It should be kept in mind that obesity can cause technical difficulties and a increased risk of complications.32‑34
Recent studies suggest that the results of unicompartmental knee arthroplasty in the younger patient group compare well with the results of total knee arthroplasty in similar age groups.33, 35, 36Non-operative management must be exhausted before surgery is contemplated. The options of high tibial osteotomy may be applicable in young patients. The advantages of unicompartmental knee arthroplasty compared with a high tibial osteotomy include higher rates of initial success and fewer early complications.37, 38Total knee arthroplasty following high tibial osteotomy is associated with poor results with more problems related to surgical exposure and more technical difficulties compared to conversion of a unicompartmental knee arthroplasty to a total knee arthroplasty.39
It is shown that the rate of revision for mobile-bearing unicompartmental knee arthroplasty undertaken for failed high tibial osteotomy is approximately nine times higher than that for primary mobile-bearing unicompartmental knee arthroplasty. Furthermore, the revision rate for mobile-bearing unicompartmental knee arthroplasty performed for failed high tibial osteotomy is higher than the revision rate of total knee arthroplasty after failed high tibial osteotomy. When the varus deformity has already been fully or partially corrected extra-articularly by a successful high tibial osteotomy, any further change in alignment from a mobile-bearing unicompartmental knee arthroplasty can cause an over-correction. This results in a valgus alignment of the leg and increased loading of the lateral compartment. It is recommended that mobile-bearing unicompartmental knee arthroplasty not be used in knees that have previously undergone a high tibial osteotomy.40
The preoperative assessment consists largely of obtaining a thorough history to ensure that the patient is a good candidate for unicompartmental knee arthroplasty. Clinical examination and radiological assessment are also required to confirm patient eligibility. Imaging studies include anteroposterior (AP, preferably in 30° of flexion) and tunnel radiographs made while the patient is standing, which can help differentiate between unicompartmental and bicompartmental or tricompartmental disease. Obtaining weight-bearing radiographs is important to assess narrowing of the cartilage. Lateral radiographs are helpful for establishing the absence of AP tibial translation with posterior bone loss. Such posterior bone loss is a contraindication for unicompartmental knee arthroplasty. The size of the femoral component should be chosen preoperatively using a (digital) X-ray template and (digital) lateral radiograph. The lateral stress AP radiographs (preferably in 20° of flexion) made with the patient supine and with valgus and then varus stress applied to the knee can unmask narrowing in the opposite compartment. Any deformity should be reducible. Digital whole-leg radiographs are obtained preoperatively while the patient is standing, to measure leg (tibiofemoral) alignment. This may also be done postoperatively for objective measurement of the correction obtained.
The patient is placed in a supine position with the draped leg placed on a thigh support or in a leg holder with tourniquet control (Fig 2). When positioning the patient, ensure that the knee is free to flex to at least 120°. The leg is draped free, and it is helpful to place a mark or ball of tape over the anterior superior iliac spine or the femoral head for the latter proximal tibial cut orientation.
Inspection of the joint is obligatory at the time of arthrotomy. Although the patient may be an ideal candidate for the procedure as indicated by clinical examination and radiography, contraindications may be discovered. The ultimate decision to continue with the unicompartmental procedure must be made based on the intra-articular findings, keeping the indications and contraindications in mind.42
All osteophytes must be removed from the medial aspects of the medial femoral condyle and the tibial plateau (Fig 3). These osteophytes often prevent passive adequate correction of the varus deformity because of a relative shortening of the capsule and medial collateral ligament as they pass over the osteophytes. The osteophytes from both margins of the intercondylar notch must be removed to allow adequate orientation for the vertical tibial saw cut. Absence of the osteophytes also facilitates adequate positioning of the femoral drill guide in the middle of the medial condyle.
With a mobile-bearing unicompartmental knee arthroplasty, the tibial cut should be just medial to the origin of the ACL, avoiding damage to its fibres. The blade is pointed towards the head of the femur (Fig 4). The assistant who palpates halfway between the pubic tubercle and the anterior superior iliac spine can demonstrate the position of the femoral head. Due to the sterile draping the orientation is not always simple. Before draping you could pinpoint the head of the femur and draw a line from the anteromedial side of the knee to the femoral head. This gives you a nice guide for the tibial cut. Some surgeons may find fluoroscopy helpful when determining the exact location of the femoral head.
The vertical saw cut should be level with the tibial saw cut; a deeper saw cut may act as a stress line and can cause a tibial plateau fracture while impacting the definitive tibial plate, or postoperatively with a trauma or a stress fracture.43, 44Before making the horizontal cut with the 12 mm-wide oscillating saw blade, the reciprocating saw could be placed in the vertical cut to evade undermining of the eminentia. When the tibial saw guide shaft is applied parallel with the long axis of the tibia in both planes, the horizontal cut will make a 7-degree slope backwards and downwards. It is generally believed that square (0 degrees) inclination is the best for mechanical stress and for clinical results. When placed in varus inclination the contact pressure may be higher45and clinical results tend to be poor.46The most stable inclination for the tibial component may be in slight valgus inclination, which results in more even stress distribution. There is however no literature showing the possible advantages of this positioning.45
The intramedullary rod is a useful guide to allow proper placement of the femoral component. In the manual of surgical technique for Oxford phase-3 unicompartmental knee arthroplasty, the allowed alignment variation is 10° varus or valgus in the coronal plane and 5° flexion or extension in the sagittal plane for the femoral component.
The femoral drill guide should ensure proper placement of the femoral component (with a 7-degree fin on the side). The femoral drill guide is visually aligned parallel to the long axis of the tibia and parallel to the intramedullary femoral rod in the coronal and sagittal planes. An uncertainty factor is induced in the positioning of the femoral drill guide, as it is not fixed to the intramedullary rod. The long intramedullary rods are more accurate due to the diameter decrease of the femur more proximal to the knee joint line. The intramedullary rod should be situated 1 cm anteriorly to the anteromedial corner of the intercondylar notch. The more you place the intramedullary rod to the lateral side, the more impingement with the patella is supposed when flexing the knee for proper placement of the femoral drill guide. A patella baja will cause more impingement and difficulties for proper placement of the femoral component.
Possible perforation of the femoral cortex with the intramedullary rod is a concern. Chances of perforation increase with the thin rod, due to its diameter. Never hammer the rod into the intramedullary canal when there is too much resistance: perforation of the femoral cortex may cause a fracture of the femur, or an arterial lesion may occur when the long rod is advanced through the perforation.
The femoral saw block is used to cut the posterior facet of the femoral condyle (Fig 5). Be sure to remove this facet so it won’t stay posterior and become a corpus librum which may cause extension deficit or impingement of the bearing and consequently dislocation of the bearing. The pressure on the posterior capsule may cause pain.
After the second milling of the femur over the spigot, all the protruding bone on the outside of the periphery of the cutting teeth should be removed. Depending on the spigot number used for the second milling, a 1- to 7-mm bone edge has to be removed around the drill hole. Because of the flange on the spigot the mill does not remove the bone under the flange. When this bone is not removed, the femoral component cannot be placed flush to the milled condyle, causing a misbalance in flexion and extension.
The flexion gap is measured with the leg in 90° of flexion. The feeler gauge thickness between the femoral and tibial components is correct when the natural tension in the ligaments is achieved. The feeler gauge will slide in and out easily without too much compression between the two fingers holding the gauge. The feeler gauge should be removed before measuring the extension gap. The extension gap is usually narrower and extension with the thick gauge will stretch the medial collateral ligament. This may lead to postoperative valgus by placing a thicker mobile bearing to achieve the right medial ligament tension. In full extension the posterior capsule is tight and gives under measurement of the extension gap; 20° of flexion of the knee eliminates this influence and is advised to measure the extension gap.
The cortex is a very important issue in the preparation and positioning of the tibial plateau. While preparing the groove for the tibial keel, the anterior and posterior cortices should not be damaged (Fig 6). When the cortex is damaged cement spill can occur, especially on the posterior border. Interrupted cortex may act as a stress point and increase the risk of a tibial plateau fracture while impacting the tibial implant.
The cortex is also the support for the tibial plateau. The posterior edge of the tibial plateau has to rest on the posterior cortex. When flexing the knee, the mobile bearing moves posteriorly and consequently the load moves posteriorly. When the tibial plateau is only supported by its spongiosa and not by the cortex, the posterior load will cause posterior tilting of the plateau. The spongiosa is not strong enough to support the tibial component with the loads. Loosening of the tibial plateau will be the end result.
The difference between the feeler gauge and the trial bearing is the posterior lip of the trial bearing. This posterior edge is 3 mm higher. While inserting the trial bearing, the space between the tibial and femoral components is stretched 3 mm more than the measured bearing or the feeler gauge. Because of this, you may have the feeling that you should use a bigger bearing than originally measured. Use of the trial bearing should be minimised to avoid stretching of the medial collateral ligament. The consequence of a bigger bearing on the alignment of the knee is more valgus, which may cause early deterioration in the lateral compartment.
The surface of the tibia is usually not sclerotic, so there is no need for small drill holes. The femoral surface is usually very sclerotic though, and multiple small drill holes should be made for adequate fixation of the femoral component to the femur with cement (Fig. 7). Adequate cement fixation is the only constraint for the movement of the femoral component in the long axis of the femur. When there is maximum flexion, the forces of the mobile bearing push the femoral component forward when the fixation is not adequate. In extension, the forces of the mobile bearing push the femoral component back against the femur. The patient may describe this mechanism as a luxation feeling. For the cementing phase, this mechanism implies that during settling of the cement the leg should be held in 45° of flexion. When the leg is fully extended the tibial component may tilt anteriorly, when fully flexed it may tilt posteriorly.
We reiterate that use of the trial bearing should be avoided up to this point. When the tibial and femoral components are cemented with the feeler gauge in-between, the trial bearing is used thereafter. With the trial bearing in place and the knee in full extension, at least 4 mm clearance should be in front of the bearing to reduce the risk of impingement of the bearing against bone.
When inserting the definitive bearing, holding the knee in about 110° of flexion will make it easier. If you have only one version of each definitive bearing, be sure not to let it slip out of your hand, as the mobile bearing usually becomes slippery during insertion. A suggestion is to have a spare in the operating room – accidents happen.
The optimal tibiofemoral alignment following unicompartmental arthroplasty has yet to be determined. Extremes of overcorrection and undercorrection are undesirable.47Overcorrection might result in mediolateral subluxation and increased loading of the lateral compartment;5, 48‑50undercorrection results in varus alignment of the leg and will potentially overload the implant.51, 52Many experienced surgeons recommended moderate undercorrection of the mechanical axis.26, 53‑56
Computer-assisted surgery can improve the postoperative alignment of medial unicompartmental knee arthroplasty compared to conventional techniques.57, 58Real-time information about the leg axis at each step during the operation should diminish the danger of overcorrection or undercorrection. The navigation system may also be helpful in achieving a more precise component orientation,59but some research involves cadaver studies60and other saw bone studies.61The limited exposure and the restricted visual field in vivo with the minimally invasive technique makes it difficult to interpret these results for clinical use for optimal positioning of the components. Further development of the navigation technique will prove if it is more accurate than the conventional technique.
Concerns regarding infection are the same as for other arthroplasties; the standard precautions should be employed. Another concern is deep venous thrombosis (DVT). Use of low molecular weight heparin (LMWH) for 6 weeks is standard practice for preventing postoperative DVT, regardless of past history of DVT. In the United States a prophylactic anticoagulant is generally used when there is a past history of DVT, but there is a tendency to use the LMWH standard in postoperative treatment.62
Complex Regional Pain Syndrome (CRPS) is rarely mentioned in the literature after total knee arthroplasty, and not mentioned after mobile-bearing unicompartmental knee arthroplasty. We know of one patient who had CRPS diagnosed five weeks after the procedure. This patient was sent to the anaesthesiologist and got proper treatment, which in this case was manitol infusion.
The mobile bearing has it advantages but there is also a risk of dislocation. A mobile-bearing unicompartmental arthroplasty on the lateral side gives a higher dislocation rate due to the physiological ligamentous laxity on that side.63‑66The ligaments on the medial side are less elastic than those on the lateral side. Dislocation of the meniscal bearing on the medial side is technique-dependent. Misalignment of the femoral and tibial components, ligamentous release, posterior impingement from osteophytes and remnants of cartilaginous meniscus are typically causes of dislocation of the bearing.3A non-technical-related cause is a hyperflexion trauma of the knee.
The mobile bearing gives a large area of contact throughout the entire range of movement, assuring minimal polyethylene wear. The average wear rate is 0.03 mm per year.14, 67Results from an in vivo study show a mean linear wear rate of 0.02 mm/year at ten years.68The size of the bearing has no influence on the wear rate67or on the survival of the implant.2Proper alignment does have an effect on the wear rate of the mobile bearing. Bearings showing signs of impingement due to misalignment of the components have a maximum wear rate of 0.08 mm. Those bearings showing no signs of impingement have a mean wear rate of 0.01 mm per year.67
Mobilisation of the knee and patient can start on the day after surgery. Recovery of knee function is usually rapid, with considerably less pain than in a total knee replacement. Early mobilisation is encouraged, and passive assistance by the physical therapist is advised. The patient can frequently be discharged after 2-3 days. Some centres are discharging patients undergoing knee replacement within a day of surgery.4Prophylaxis against deep vein thrombosis is recommended for the duration of the hospitalisation. Post-discharge prophylaxis is at the discretion of the surgeon.
Oxford phase-3 mobile-bearing unicompartmental knee arthroplasty has been used more frequently in Europe, but it is now also gaining prominence as a standard reconstructive option in the United States. With the introduction of new techniques, new pitfalls are encountered and a learning curve exists.69The keys for achieving acceptable clinical outcomes of mobile-bearing unicompartmental knee arthroplasty are stringent patient selection, careful surgical technique and a proven prosthetic design. This mobile-bearing implant should only be used by surgeons who are appropriately trained in its use with an understanding of how to avoid common errors.10, 16To minimise errors and improve long-term follow-up, knowledge of the pitfalls, tips and tricks of this prosthesis is mandatory.
1. Murray DW, Goodfellow JW, O'Connor JJ. The Oxford medial unicompartmental arthroplasty: a ten-year survival study. J Bone Joint Surg Br 1998;80:983-9.
2. Price AJ, Waite JC, Svard U. Long-term clinical results of the medial Oxford unicompartmental knee arthroplasty. Clin Orthop Relat Res 2005:171-80.
3. Emerson RH, Jr. Unicompartmental mobile-bearing knee arthroplasty. Instr Course Lect 2005;54:221-4.
4. Beard DJ, Murray DW, Rees JL, Price AJ, Dodd CA. Accelerated recovery for unicompartmental knee replacement--a feasibility study. Knee 2002;9:221-4.
5. Fisher DA, Watts M, Davis KE. Implant position in knee surgery: a comparison of minimally invasive, open unicompartmental, and total knee arthroplasty. J Arthroplasty 2003;18:2-8.
6. Fuchs S, Rolauffs B, Plaumann T, Tibesku CO, Rosenbaum D. Clinical and functional results after the rehabilitation period in minimally-invasive unicondylar knee arthroplasty patients. Knee Surg Sports Traumatol Arthrosc 2005;13:179-86.
7. Hassaballa MA, Porteous AJ, Newman JH. Observed kneeling ability after total, unicompartmental and patellofemoral knee arthroplasty: perception versus reality. Knee Surg Sports Traumatol Arthrosc 2004;12:136-9.
8. Jahromi I, Walton NP, Dobson PJ, Lewis PL, Campbell DG. Patient-perceived outcome measures following unicompartmental knee arthroplasty with mini-incision. Int Orthop 2004;28:286-9.
9. Repicci JA, Hartman JF. Minimally invasive unicondylar knee arthroplasty for the treatment of unicompartmental osteoarthritis: an outpatient arthritic bypass procedure. Orthop Clin North Am 2004;35:201-16.
10. Robertsson O, Knutson K, Lewold S, Lidgren L. The routine of surgical management reduces failure after unicompartmental knee arthroplasty. J Bone Joint Surg Br 2001;83:45-9.
11. Jenny JY. Navigated unicompartmental knee replacement. Orthopedics 2005;28:s1263-7.
12. Jeer PJ, Keene GC, Gill P. Unicompartmental knee arthroplasty: an intermediate report of survivorship after the introduction of a new system with analysis of failures. Knee 2004;11:369-74.
13. Goodfellow JW, Tibrewal SB, Sherman KP, O'Connor JJ. Unicompartmental Oxford Meniscal knee arthroplasty. J Arthroplasty 1987;2:1-9.
14. Argenson JN, O'Connor JJ. Polyethylene wear in meniscal knee replacement. A one to nine-year retrieval analysis of the Oxford knee. J Bone Joint Surg Br 1992;74:228-32.
15. Murray DW. Mobile bearing unicompartmental knee replacement. Orthopedics 2005;28:985-7.
16. Svard UC, Price AJ. Oxford medial unicompartmental knee arthroplasty. A survival analysis of an independent series. J Bone Joint Surg Br 2001;83:191-4.
17. Price AJ, Webb J, Topf H, Dodd CA, Goodfellow JW, Murray DW. Rapid recovery after oxford unicompartmental arthroplasty through a short incision. J Arthroplasty 2001;16:970-6.
18. Pandit H, Jenkins C, Barker K, Dodd CA, Murray DW. The Oxford medial unicompartmental knee replacement using a minimally-invasive approach. J Bone Joint Surg Br 2006;88:54-60.
19. Carr A, Keyes G, Miller R, O'Connor J, Goodfellow J. Medial unicompartmental arthroplasty. A survival study of the Oxford meniscal knee. Clin Orthop Relat Res 1993:205-13.
20. Cartier P, Cheaib S. Unicondylar knee arthroplasty. 2-10 years of follow-up evaluation. J Arthroplasty 1987;2:157-62.
21. Langdown AJ, Pandit H, Price AJ, Dodd CA, Murray DW, Svard UC, et al. Oxford medial unicompartmental arthroplasty for focal spontaneous osteonecrosis of the knee. Acta Orthop 2005;76:688-92.
22. Goodfellow J, O'Connor J. The mechanics of the knee and prosthesis design. J Bone Joint Surg Br 1978;60-B:358-69.
23. White SH, Ludkowski PF, Goodfellow JW. Anteromedial osteoarthritis of the knee. J Bone Joint Surg Br 1991;73:582-6.
24. Goodfellow J, O'Connor J. The anterior cruciate ligament in knee arthroplasty. A risk-factor with unconstrained meniscal prostheses. Clin Orthop Relat Res 1992:245-52.
25. Goodfellow J, O'Connor J, Murray DW. The Oxford meniscal unicompartmental knee. J Knee Surg 2002;15:240-6.
26. Cartier P, Sanouiller JL, Grelsamer RP. Unicompartmental knee arthroplasty surgery. 10-year minimum follow-up period. J Arthroplasty 1996;11:782-8.
27. Corpe RS, Engh GA. A quantitative assessment of degenerative changes acceptable in the unoperated compartments of knees undergoing unicompartmental replacement. Orthopedics 1990;13:319-23.
28. Markel DC, Sutton K. Unicompartmental knee arthroplasty: troubleshooting implant positioning and technical failures. J Knee Surg 2005;18:96-101.
29. Thornhill TS, Scott RD. Unicompartmental total knee arthroplasty. Orthop Clin North Am 1989;20:245-56.
30. Robertsson O, Knutson K, Lewold S, Goodman S, Lidgren L. Knee arthroplasty in rheumatoid arthritis. A report from the Swedish Knee Arthroplasty Register on 4,381 primary operations 1985-1995. Acta Orthop Scand 1997;68:545-53.
31. Woods DA, Wallace DA, Woods CG, McLardy-Smith P, Carr AJ, Murray DW, et al. Chondrocalcinosis and medial unicompartmental knee arthroplasty. The Knee 1995;2:117-9.
32. Berend KR, Lombardi AV, Jr., Mallory TH, Adams JB, Groseth KL. Early failure of minimally invasive unicompartmental knee arthroplasty is associated with obesity. Clin Orthop Relat Res 2005;440:60-6.
33. Tabor OB, Jr., Tabor OB, Bernard M, Wan JY. Unicompartmental knee arthroplasty: long-term success in middle-age and obese patients. J Surg Orthop Adv 2005;14:59-63.
34. Tabor OB, Jr., Tabor OB. Unicompartmental arthroplasty: a long-term follow-up study. J Arthroplasty 1998;13:373-9.
35. Pennington DW, Swienckowski JJ, Lutes WB, Drake GN. Unicompartmental knee arthroplasty in patients sixty years of age or younger. J Bone Joint Surg Am 2003;85-A:1968-73.
36. Swienckowski JJ, Pennington DW. Unicompartmental knee arthroplasty in patients sixty years of age or younger. J Bone Joint Surg Am 2004;86-A Suppl 1:131-42.
37. Jackson RW. Surgical treatment. Osteotomy and unicompartmental arthroplasty. Am J Knee Surg 1998;11:55-7.
38. Ivarsson I, Gillquist J. Rehabilitation after high tibial osteotomy and unicompartmental arthroplasty. A comparative study. Clin Orthop Relat Res 1991:139-44.
39. Hanssen AD, Stuart MJ, Scott RD, Scuderi GR. Surgical options for the middle-aged patient with osteoarthritis of the knee joint. Instr Course Lect 2001;50:499-511.
40. Rees JL, Price AJ, Lynskey TG, Svard UC, Dodd CA, Murray DW. Medial unicompartmental arthroplasty after failed high tibial osteotomy. J Bone Joint Surg Br 2001;83:1034-6.
41. Kort NP, Raay JJAM, Romanowski M. Unicompartmental Knee Arthroplasty. Emedicine web site http://www.emedicine.com/orthoped/topic631.htm.
42. Scott RD, Santore RF. Unicondylar unicompartmental replacement for osteoarthritis of the knee. J Bone Joint Surg Am 1981;63:536-44.
43. Yang KY, Yeo SJ, Lo NN. Stress fracture of the medial tibial plateau after minimally invasive unicompartmental knee arthroplasty: a report of 2 cases. J Arthroplasty 2003;18:801-3.
44. Brumby SA, Carrington R, Zayontz S, Reish T, Scott RD. Tibial plateau stress fracture: a complication of unicompartmental knee arthroplasty using 4 guide pinholes. J Arthroplasty 2003;18:809-12.
45. Iesaka K, Tsumura H, Sonoda H, Sawatari T, Takasita M, Torisu T. The effects of tibial component inclination on bone stress after unicompartmental knee arthroplasty. J Biomech 2002;35:969-74.
46. Swienckowski J, Page BJ, 2nd. Medial unicompartmental arthroplasty of the knee. Use of the L-cut and comparison with the tibial inset method. Clin Orthop Relat Res 1989:161-7.
47. Kennedy WR, White RP. Unicompartmental arthroplasty of the knee. Postoperative alignment and its influence on overall results. Clin Orthop Relat Res 1987:278-85.
48. Deshmukh RV, Scott RD. Unicompartmental knee arthroplasty: long-term results. Clin Orthop Relat Res 2001:272-8.
49. Squire MW, Callaghan JJ, Goetz DD, Sullivan PM, Johnston RC. Unicompartmental knee replacement. A minimum 15 year followup study. Clin Orthop Relat Res 1999:61-72.
50. Gioe TJ, Killeen KK, Hoeffel DP, Bert JM, Comfort TK, Scheltema K, et al. Analysis of unicompartmental knee arthroplasty in a community-based implant registry. Clin Orthop Relat Res 2003:111-9.
51. Ridgeway SR, McAuley JP, Ammeen DJ, Engh GA. The effect of alignment of the knee on the outcome of unicompartmental knee replacement. J Bone Joint Surg Br 2002;84:351-5.
52. Emerson RH, Jr., Head WC, Peters PC, Jr. Soft-tissue balance and alignment in medial unicompartmental knee arthroplasty. J Bone Joint Surg Br 1992;74:807-10.
53. Argenson JN, Chevrol-Benkeddache Y, Aubaniac JM. Modern unicompartmental knee arthroplasty with cement: a three to ten-year follow-up study. J Bone Joint Surg Am 2002;84-A:2235-9.
54. Ansari S, Newman JH, Ackroyd CE. St. Georg sledge for medial compartment knee replacement. 461 arthroplasties followed for 4 (1-17) years. Acta Orthop Scand 1997;68:430-4.
55. Engh GA, McAuley JP. Unicondylar arthroplasty: an option for high-demand patients with gonarthrosis. Instr Course Lect 1999;48:143-8.
56. Hernigou P, Deschamps G. Alignment influences wear in the knee after medial unicompartmental arthroplasty. Clin Orthop Relat Res 2004:161-5.
57. Keene G, Simpson D, Kalairajah Y. Limb alignment in computer-assisted minimally-invasive unicompartmental knee replacement. J Bone Joint Surg Br 2006;88:44-8.
58. Cossey AJ, Spriggins AJ. The use of computer-assisted surgical navigation to prevent malalignment in unicompartmental knee arthroplasty. J Arthroplasty 2005;20:29-34.
59. Perlick L, Bathis H, Tingart M, Perlick C, Luring C, Grifka J. Minimally invasive unicompartmental knee replacement with a nonimage-based navigation system. Int Orthop 2004;28:193-7.
60. Aldinger PR, Gill HS, Schlegel U, Schneider M, Clauss M, Goodfellow JW, et al. [Is computernavigation a usefull tool in unicompartmental knee arthroplasty? A pilot cadaver study.]. Orthopade 2005;34:1094-102.
61. Mayman DJ, Rudan J, Watson D, Ellis R. Computer-enhanced insertion of the Oxford unicompartmental arthroplasty: a fluoroguide technique. Comput Aided Surg 2004;9:81-5.
62. Lieberman JR, Hsu WK. Prevention of venous thromboembolic disease after total hip and knee arthroplasty. J Bone Joint Surg Am 2005;87:2097-112.
63. Weale AE, Feikes J, Prothero D, O'Connor JJ, Murray D, Goodfellow J. In vitro evaluation of the resistance to dislocation of a meniscal-bearing total knee prosthesis between 30 degrees and 90 degrees of knee flexion. J Arthroplasty 2002;17:475-83.
64. Robinson BJ, Rees JL, Price AJ, Beard DJ, Murray DW, McLardy Smith P, et al. Dislocation of the bearing of the Oxford lateral unicompartmental arthroplasty. A radiological assessment. J Bone Joint Surg Br 2002;84:653-7.
65. Robinson BJ, Rees JL, Price AJ, Beard DJ, Murray DM. A kinematic study of lateral unicompartmental arthroplasty. Knee 2002;9:237-40.
66. Gunther T, Murray DW, Miller R, Wallace DA, Carr AJ, O'Connor JJ. Lateral unicompartmental arthroplasty with the Oxford meniscal knee. Knee 1996;3:33-9.
67. Psychoyios V, Crawford RW, O'Connor JJ, Murray DW. Wear of congruent meniscal bearings in unicompartmental knee arthroplasty: a retrieval study of 16 specimens. J Bone Joint Surg Br 1998;80:976-82.
68. Price AJ, Short A, Kellett C, Beard D, Gill H, Pandit H, et al. Ten-year in vivo wear measurement of a fully congruent mobile bearing unicompartmental knee arthroplasty. J Bone Joint Surg Br 2005;87:1493-7.
69. Rees JL, Price AJ, Beard DJ, Dodd CA, Murray DW. Minimally invasive Oxford unicompartmental knee arthroplasty: functional results at 1 year and the effect of surgical inexperience. Knee 2004;11:363-7.
Paramedical skin incision.
A thigh tourniquet is applied and the leg is placed on a thigh support.
Large osteophytes should be removed.
The blade is pointed towards the femoral head.
The posterior facet of the femoral condyle should be excised.
Take care that the dorsal and ventral cortices remain intact.
The femoral surface is roughened bij multiple small drill holes.