Healio
Healio
October 01, 2006
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Navigated Minimally Invasive Unicompartmental Knee Arthroplasty

Abstract

Unicompartmental knee arthroplasty (UKA) is an alternative procedure to high tibial osteotomy. This study assessed the procedure using computer navigation to improve implantation accuracy and presents early radiological results of a group of patients implanted with the univation UKA (B. Braun Aesculap, Tuttlingen, Germany) with navigation instrumentation and a minimally invasive approach. The authors concluded that navigated implantation of a UKA using a nonimage-based system improved radiologic accuracy implantation without significant inconvenience and minimal change in the conventional operating technique.

Implantation accuracy is a prognostic factor for long-term unicompartmental knee arthroplasty (UKA) survival.1-3 Most UKA systems offer limited and potentially inaccurate instrumentation that relies substantially on a surgeon’s judgment for correct implant positioning. Rates of inaccurate implantations as high as 30% have been reported with conventional, free-hand instrumentation.4 Intramedullary femoral guiding devices can improve the results but do not guarantee reproducible optimal implantation.5,6

Computer-assisted systems for total knee arthroplasty (TKA) result in greater implant positioning precision compared with conventional instrumentations.7-9 The OrthoPilot system (B. Braun Aesculap, Tuttlingen, Germany) is a nonimage-based system that relies on intraoperative kinematic analyses of lower limbs and has been clinically validated following a prospective, randomized study.10

Minimally invasive surgical (MIS) techniques were developed to decrease surgical trauma. In addition, evidence suggests that MIS techniques might decrease hospitalization time postoperatively, because it facilitates postoperative rehabilitation.11 A study also showed that MIS techniques improve functional scores after 1 year and do not lead to significant implantation accuracy loss compared with the standard open approach.12 A new implant was developed (univation, B. Braun Aesculap) with an extra-articular resection guide fixation to further decrease invasiveness associated with the procedure and to facilitate navigation. The implantation side of the metallic femoral component is cylindrical, whereas the articular surface is spherical and designed to obtain contact between the articular surface and the meniscal bearing throughout the entire range of motion. The meniscal polyethylene bearing has a proximal surface perfectly congruent with the femoral component and a flat inferior surface congruent with the metallic tibial tray. Both metallic components are designed for cemented implantation.

This study reports early radiologic results of a group of patients implanted with the univation UKA with navigation instrumentation and an MIS approach.

An historical control group of patients were implanted with Oxford III UKA (Biomet, Berlin, Germany) using conventional instrumentation and an MIS approach.

figure 1

figure 2

Figure 1: Minimally invasive non-navigated technique: tibial resection. Figure 2: Minimally-invasive navigated technique tibial resection.

Operative Techniques

In the MIS non-navigated technique, the Oxford III UKA was implanted according to the instructions of the manufacturer (Figures 1-3). Before implantation, the patient’s leg was placed in an arthroscopy leg fixation with a tourniquet in typical position. A medial parapatellar cut, typically 8 cm long, was performed.

First, surgeons used a cutting guide to ablate the tibial bone. The resection level of the distal femur was subsequently determined by intramedullary or extramedullary orientation. After a posterior cut, the femur was prepared with a rotational mill until flexion and extension were accurately balanced. The cementing of the original tibial component and the femoral component followed trial reposition.

figure 3a

figure 3b

Figure 3: Measurement of the implant position (univation), instructions by the manufacturer (A). Measurement of the implant position (Oxford III), instructions by the manufacturer (B).

In the MIS orthopedic solution technique, the nonimage-based OrthoPilot navigation system was used (Figure 2).13-15 The surgeons used a medial parapatellar incision, typically 8 cm long, and screwed two infrared localizers into the distal femur and proximal tibia; an additional localizer was strapped onto the dorsum of the foot. A Polaris infrared camera (Northern Digital, Toronto, Canada) tracked the relative motion of two adjacent localizers and calculated rotations of the hip, knee, and ankle joints. The mechanical axes of the femur and tibia on coronal and sagittal planes were calculated with data recorded from the infrared camera.

The infrared camera also displayed the orientation of a localizer fixed on the tibial or femoral resection blocks and compared the positions with the mechanical bone axes. The tibial resection was performed with a conventional motorized saw blade guided with a free-hand navigated orientation device, and the femoral resection was performed with a box fixed to the distal femur with two percutaneous screws. The bow was navigated along the knee flexion axis and was secured with the femur guide without direct fixation to the joint. A milling device was used to perform a distal femoral resection.

table 1

Materials and Methods

The non-navigated group consisted of patients with primary osteoarthritis of the medial knee compartment who underwent surgery at the Department of Orthopedic Surgery, Grosshadern Medical Center, University of Munich, between 1999 and 2005. Experienced knee surgeons performed all implantations.

Implantations of navigated prostheses were performed at four hospitals in this multicenter trial between October 2005 and April 2006 by experienced reconstructive knee surgeons. Detailed data regarding patient age, sex, and the number of surgeons are shown in Table 1.

Standard anteroposterior (AP) and lateral radiographs determined the accuracy of implant positioning. Evaluation was performed according to the manufacturers’ specifications (Figure 3) as well as the percentage of implant positions outside the optimal range (Table 2). The optimal implant position is influenced by navigation, implant size, and the individual surgeon. Only the criteria depending on the navigation and implant size were evaluated.

table 2

Results

The authors assessed radiologically the implant position angles , , , and (Table 3). The navigated implantation results of the femoral varus-valgus position of the prosthesis () were slightly superior to the standard MIS implantation (2% versus 7%, out of range).

Navigated implantation results were superior to the results for the non-navigated group (25% versus 51%, out of range) for femoral flexion-extension position (), despite 25% of these knees not being in an optimal position.

table 3

In the first surgical patients, only femoral component preparation was navigated. A new instrument that permitted the navigated femoral component implantation was introduced during the last 10 implantations and with this device, 9 of 10 femoral components (90%) were in the manufacturers’ optimal range.

Results for the tibial slope () were better in the navigated group than in the non-navigated group (7% versus 10% of the implants out of range).

The varus-valgus position for the tibia () was nearly identical in both groups. In the univation group, 2% were out of the optimal range, compared with 1% in the Oxford group. The criteria compared the navigation technique with the non-navigated technique. The authors assessed radiologically the size of the implant compared with the size of the bone (Table 3).

The posterior distance between the implant and the femoral condyle (A) was 18% (range: -2 mm-4 mm) out of range of the navigated group and 35% (range: -3 mm-8 mm) of the standard group. The size of the tibial implant was not always accurate. In 37% of the cases, the implant was more than 2 mm too small for posterior fitting (F), and the same problem occurred in 17% of the cases for the anterior fitting (G). In contrast, the tibial plateau (H) medial border had an overhang of >2 mm (28%). Here, the results for the Oxford group were better than those for the univation group (Table 3).

Discussion

Navigation systems have improved TKA implantation accuracy.7-10,16 The precision of the system used in this study was experimentally calculated to be 1° for angle measurements and 1 mm for distance measurements.17 However, outliers still can occur. Several possible additional reasons for observed system errors include lack of radiologic measurement technique precision, lack of rigid resection block fixation onto the bone, and lack of precise saw blade guiding, including bending saw blades over the resection blocks.18

Unicompartmental knee arthroplasty is a valuable alternative to high tibial osteotomy;19 TKA is the preferred surgery for patients with isolated medial osteoarthritis.4,18,20-23 The exact indications are still controversial because some authors report low UKA and TKA implant survival rates.24 Inaccurate implantation often results in early failure.1,3 General agreement on the ideal positioning of a UKA does not exist, and the positioning in this study was achieved according to the authors’ clinical opinion.

The goal of instrumentation, however, is to allow the surgeon to place the prosthesis as accurately as possible in optimal position. Most instrumentations have imprecise guiding systems and do not guarantee a reproducible and optimal implantation technique.5,6 The conventional navigated instrumentation used in Jenny and Boeri’s13 study was similar to the instrumentation used for TKA implantation and achieved a higher implantation rate into the desired angular range on postoperative radiography compared with the manual technique. The instrumentation also generated a significantly higher rate of globally satisfactory implantations, with all measured angles within the desired range. The rates were similar to those obtained with the reference TKA software.

Conventional navigation techniques involve conventional skin incisions and approaches, with the splitting of the vastus medialis muscle and lateral subluxation of the patella. The authors developed a navigated minimally invasive technique, which allows performing the procedure through a shorter skin incision of 7 cm to 10 cm, which is relevant because not dislocating the patella and leaving the extensor mechanism intact at the suprapatellar pouch is a significant indicator of functional outcome.12

The authors compared the radiologic implantation accuracy of a minimally invasive approach in the first 49 navigated implantations with a minimally invasive approach in 87 non-navigated prosthesis implantations, the Oxford III. The Oxford UKA was chosen as a reference because it is implanted frequently, has long-term results and has a survival rate of 9 to 10 years (reported to be between 95% and 99.1%).25-28

The femoral component orientation in the AP view () was superior, and was 98% versus 93% accurate in the Oxford group. In addition to achieving good results, the femoral component is designed as a sphere, which is very forgiving concerning malpositioning. The results in the extension-flexion angle () of the femoral component were not successful in the first implantations but still improved compared with the Oxford group (76% versus 49% in the non-navigated group). In comparison with the Oxford knee with a large stem, the univation has short teeth for femoral fixation. The advantage of the univation knee is better bone stock in revision surgery, but a potential disadvantage is the suboptimal orientation during implantation, because the short teeth are covered with cement. Therefore, a new instrument was introduced to permit accurate navigated femur component implantation. Nine correct positionings in the last 10 implantations were achieved with the new enhancement and were confirmed in the next implantation series.

Tibial slope () results in the navigated group were better than in the non-navigated group, but were still 7% out of range. The optimal range noted by the manufacturer (84°-90°) was very narrow, especially in comparison with the optimal range for the Oxford group (-5° to -7°). The range of the slope for the navigated group was between 83° and 93°. Using the Oxford criteria, all navigated implantations (100%) would have been in the optimal range. At this time, the optimal slope is still not clearly defined. A wide, interindividual range of slope angles exists, and the question is whether the slope should be orientated patient-specific or implant-specific.

The positioning of the tibial component in the AP view () is nearly identical in both groups, with good results of 99% in the non-navigated group and 98% in the navigated group.

The navigated group consists of the implantations performed in the four centers, including the first implantations with the navigation technique for the new developed unicondylar MIS-prosthesis. In every center, the surgeons saw a greater accuracy in the implant positioning in the last implantations compared with the earlier implantations. They concluded that even for an experienced surgeon, there is a learning curve for unicondylar prosthesis, navigation, and MIS.

The authors did not study the influence of the minimally invasive approach on rehabilitation time. Research suggests minimally invasive procedures might allow earlier patient hospital discharge and faster rehabilitation.

The follow-up of the navigated prostheses is currently too short to assess any differences in clinical outcome or implant survival rates. Longer follow-up is required to determine the respective advantages and disadvantages of these techniques and the potential benefit of a minimally invasive implantation.

Conclusion

Navigated implantation of a UKA using a nonimage-based system improved radiologic accuracy implantation without significant inconvenience and minimal change in the conventional operating technique. The navigated implantation, even if more accurate than the non-navigated implantation, was not optimal by all the criteria, primarily because of a learning curve. Some innovations, however, will probably bring additional improvement. Minimally invasive implantation was effective, but it still needs to be validated on a larger scale. Long-term results with regard to function and survival time of the prosthesis also require future investigation.

References

  1. Cartier P, Sanouillier JL, Grelsamer RP. Unicompartmental knee arthroplasty surgery. 10-year minimum follow-up period. J Arthroplasty. 1996; 11:782-788.
  2. Hernigou P, Deschamps G. Prothèses unicompartimentales du genou. Rev Chir Orthop. 1996; 82(suppl)1:23.
  3. Lootvoet L, Burton P, Himmer O, et al. Prothèses unicompartimentales de genou: influence du positionnement du plateau tibial sur les résultats fonctionnels. Acta Orthop Belg. 1997; 63:94-101.
  4. Tabor OB Jr, Tabor OB. Unicompartmental arthroplasty: a long-term follow-up study. J Arthroplasty. 1998; 13:373-379.
  5. 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; 84:2235-2239.
  6. Jenny JY, Boeri C. Accuracy of implantation of a unicompartmental total knee arthroplasty with 2 different instrumentations: a case-controlled comparative study. J Arthroplasty. 2002; 17:1016-1020.
  7. Decking R, Markmann Y, Fuchs J, et al. Leg axis after computer-navigated total knee arthroplasty: a prospective randomized trial comparing computer-navigated and manual implantation. J Arthroplasty. 2005; 20:282-288.
  8. Stockl B, Nogler M, Rosiek R, et al. Navigation improves accuracy of rotational alignment in total knee arthroplasty. Clin Orthop Relat Res. 2004; 426:180-186.
  9. Victor J, Hoste D. Image-based computer-assisted total knee arthroplasty leads to lower variability in coronal alignment. Clin Orthop Relat Res. 2004; 428:131-139.
  10. Saragaglia D, Picard F, Chaussard C, et al. Mise en place des prothèses totales du genou assistée par ordinateur : comparaison avec la technique conventionelle. Rev Chir Orthop. 2001; 87:18-28.
  11. Price AJ, Webb J, Topf H, et al. Rapid recovery after Oxford unicompartmental arthroplasty through a short incision. J Arthroplasty. 2001; 16:970-976.
  12. Muller PE, Pellengahr C, Witt M, et al. Influence of minimally invasive surgery on implant positioning and the functional outcome for medial unicompartmental knee arthroplasty. J Arthroplasty. 2004; 19:296-301.
  13. Jenny JY, Boeri C. Unicompartmental knee prosthesis implantation with a nonimage-based navigation system: rationale, technique, case-control comparative study with a conventional instrumented implantation. Knee Surg Sports Traumatol Arthrosc. 2003; 11:40-45.
  14. Jenny JY, Boeri C. Computer-assisted implantation of a total knee arthroplasty: a case-control comparative study with classical instrumentation. Comput Aided Surg. 2001; 6:217-220.
  15. Ahlback S. Osteoarthrosis of the knee. A radiographic investigation. Acta Radiol Diagn. 1968; 277(suppl):7-72.
  16. Jenny JY, Boeri C. Implantation d’une prothèse totale de genou assistée par ordinateur. Etude comparative cas-témoin avec une instrumentation traditionnelle. Rev Chir Orthop. 2001; 87:645-652.
  17. Delp SL, Stulberg SD, Davies B, et al. Computer assisted knee replacement. Clin Orthop Relat Res. 1998; 354:49-56.
  18. Plaskos C, Hodgson AJ, Inkpen K, MacGraw RW. Bone cutting errors in total knee arthroplasty. J Arthroplasty. 2002; 17:698-705.
  19. Schai PA, Suh JT, Thornhill TS, Scott RD. Unicompartmental knee arthroplasty in middle-aged patients: a 2- to 6-year follow-up evaluation. J Arthroplasty. 1998; 13:365-372.
  20. Newman JH, Ackroyd CE, Shah NA. Unicompartmental or total knee replacement? Five-year results of a prospective, randomised trial of 102 osteoarthritic knees with unicompartmental arthritis. J Bone Joint Surg Br. 1998; 80:862-865.
  21. Robertsson O, Borgquist L, Knuston K, et al. Use of unicompartmental instead of tricompartmental prostheses for unicompartmental arthrosis in the knee is a cost-effective alternative. 15,437 primary tricompartmental prostheses were compared with 10,624 primary medial or lateral unicompartmental prostheses. Acta Orthop Scand. 1999; 70:170-175.
  22. Robertsson O, Dunbar M, Pehrsson T, et al. Patient satisfaction after knee arthroplasty: a report on 27,372 knees operated on between 1981 and 1995 in Sweden. Acta Orthop Scand. 2000; 71:262-267.
  23. Squire MW, Callaghan JJ, Goetz DD, et al. Unicompartmental knee replacement. A minimum 15-year follow-up study. Clin Orthop Relat Res. 1999; 367:61-72.
  24. Bert JM. 10-year survivorship of metal-backed, unicompartmental arthroplasty. J Arthroplasty. 1998; 13:901-905.
  25. Berger RA, Nedeff DD, Barden RM, et al. Unicompartmental knee arthroplasty. Clinical experience at 6- to 10-year followup. Clin Orthop Relat Res. 1999; 367:50-60.
  26. Carr A, Keyes G, Miller R, et al. Medial unicompartmental arthroplasty. A survival study of the Oxford meniscal knee. Clin Orthop Relat Res. 1993; 295:205-213.
  27. Murray DW, Goodfellow JW, O’Connor JJ. The Oxford medial unicompartmental arthroplasty: a ten-year survival study. J Bone Joint Surg Br. 1998; 80:983-989.
  28. Svard UC, Price AJ. Oxford medial unicompartmental knee arthroplasty. A survival analysis of an independent series. J Bone Joint Surg Br. 2001; 83:191-194.

Authors

Drs Jenny and Ciobanu are from the Centre de Traumatologie et d’Orthopédie, Strasbourg, France; Drs Müller, Weber, Jansson are from the Klinikum Grosshadern, Ludwig-Maximilians-Universität Munich and the Orthopädische Klinik und Poliklinik, Munich; Drs Weyer, Schmitz, and Bacher are from the Allgemeine Orthopädie, Krankenhaus für Sportverletzte Hellersen, Lüdenscheid; and Drs John and Neumann are from the Orthopädische Klinik, Otto-von-Guericke-Universität, Magdeburg, Germany.

*Drs Jenny and Müller contributed equally to this work.