1 Introduction

Unicompartmental knee replacement arthroplasty (UKA) is surgical method that only one part of knee is selectively replaced. Since mid-1990s, development of surgical method and prostheses lead to increase of UKA cases. Compared with Total knee replacement arthroplasty (TKA) in degenerative knee arthritis, UKA minimizes bone resection and conserves cruciate ligament and knee-patella joint so that physiologic functions are still remained.^1,16 Also 15 to 10 years of survival rate of UKA is comparable to TKA and good results are reported.^2,15 However, long-term results of UKA are not published yet and there are still some controversies about indication range, clinical results and so on.^3,4 The most common cause of UKA failure is due to complications associated with wear of polyethylene. To prevent these kind of complications, reduction of ligament balance and exact lower limb arrangement are important.^5,6 If this balance is not made up, there are possibilities of prostheses dissociation, wear or damage of implant⁷ and progression of arthritis of unplaced area.⁸

Authors think that use of C-arm fluoroscope in unicompartmental knee replacement arthroplasty can help to make exact balance and arrangement of lower limb so that complications associated with unbalance can be decreased. Through radiological and clinical evaluation, we studied the effectiveness of C-arm fluoroscope in unicompartmental knee replacement arthroplasty.

2 Materials and methods

2.2

2.2 Surgical method

All cases were done in supine position. Through small medial longitudinal incision, We used extramedullary guided technique with minimally invasive surgical method and prostheses were Zimmer^® Unicompartmental High Flex Knee System (Zimmer Inc, Warsaw, Ind). Under the extramedullary guidance, we used C-arm fluoroscope to check out position of guide which placed in knee and ankle joint before excision of medial tibia (Fig. 1). After excision of tibia, we took C-arm X-ray of Knee AP and LATERAL to find out the MPTA (Medial proximal tibial angle) and PTSA (posterior tibial slope angle) (Fig. 2). By using spacer block and guide, we identified the arrangement of lower leg before resection of femoral part through spacer block technique (Fig. 3). After implanting the prostheses, we checked out position of prostheses and status of arrangement by using C-arm fluoroscope (Fig. 4).

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Fig. 1 Fluoroscopic measurement of knee and ankle joint before tibia cutting by extramedullary guide.

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Fig. 2 Anteroposterior and lateral fluoroscope view after tibia cutting for check the medial proximal tibial angle and posterior tibial slope.

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Fig. 3 Alignment recheck by spacer block and extramedullary guide.

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Fig. 4 Final checking the alignment by fluoroscope after prothesis insertion.

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2.3

2.3 Radiologic evaluation

We measured femoro-tibial angle (FTA), medial proximal tibial angle (MPTA), posterior tibial slope angle(PTSA), femoral component coronal rotation angle (FCRA) by simple X-ray. We comparatively analyzed femur and tibia varus/valgus mismatch and posterior slope mismatch by above parameters after operation in group A and B. FTA(Femoro-tibial angle) was measured by Bauer⁹ method based on Knee standing AP X-ray. FTA(femoro-tibial angle) was measured by two longitudinal axis which cross over each other to make acute angle. The one is composed of mid-point of femur shaft which is 10 cm above of knee joint and mid-point of femur metaphysis which is 4 cm above of knee joint. The other is composed of mid-110 point of tibia shaft which is 4 cm below knee joint and mid-point of tibia metaphysis which is 4 cm below knee joint. Bowleg was indicated negative angle and knock-knee was indicated positive angle (Fig. 5). MPTA (medial proximal tibial angle) was measured based on knee standing AP X-ray. Same method as FTA, we measured the angle which was composed of anatomical axis of tibia and vertical axis of medial condylar tibia plateau. After UKA, MPTA was measured by anatomical axis of tibia and vertical axis of tibia prostheses (Fig. 6). PTSA (posterior tibial slope angle) was measured based on simple knee lateral X-ray and we used method described by Brandon et al.¹¹ We measured angle made by two axis. The one tibia longitudinal line is made up of mid-point of AP diameter just below tibia tubercle and mid-point of AP diameter which is 5 cm below tibia tubercle. The other axis is vertical line of medial condylar tibia plateau. After surgery we measured PTSA based on tibia anatomical longitudinal axis and under-line of tibia prostheses (Fig. 7).

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Fig. 5 Pre and postoperative measurement of femoro-tibial angle. The subsequent two points on the femur and two points on the tibia were connected. The angle subtended between these two lines was the FTA.

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Fig. 6 Pre and postoperative measurement of medial proximal tibial angle. The varus/valgus alignments of the tibial components were measured relative to the long axis of the tibia.

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Fig. 7 Pre and postoperative measurement of posterior tibial slope angle. The PTS angle is defined as 90° minus the angle made by the intersection of the line along the longitudinal axis of the tibia and the slope of the medial tibial plateau.

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After surgery, we used knee standing AP X-ray to measure FCRA(femoral component coronal rotation angle) for evaluation of varus & valgus arrangement. Longitudinal anatomical axis of tibia and femur prostheses longitudinal axis were used to measure FCRA. If distal part of femur prostheses is medially rotated, we defined varus¹² (Fig. 8).

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Fig. 8 Anteroposterior standing radiograph after the operation showing alignment of the femoral component against the long axis of the tibia.

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Also, we standardized disarrangement based on study by Gulati et al.¹³ After surgery, we evaluated varus-valgus of femur and tibia and disarrangement of posterior tibial slope angle (PTSA). Normal range of tibia varus-valgus is 87 ± 3 °, femur varus/valgus is 0 ± 3° and posterior tibial slope angle (PTSA) is 7 ± 3°. If varus/valgus is 0 ± 3° and posterior tibial slope angle (PTSA) is 7 ± 3°. If these values are beside the point, we evaluated it disarrangement.

All the pictures are used by Picture archiving and communication system(PACS) and two independent observers measured knee X-ray to reduce error of measures.

3 Results

According to the radiologic results, in group A, FTA (femoro-tibial angle) average changes from −0.6° to 6.1°, MPTA (medial proximal tibial angle) changes from 84.5° to 87.6°, PTSA (posterior tibial slope angle) changes from 6.2° to 5.2° through operation. In group B, FTA changes from −0.4° to 5.8°, MPTA changes from 84.7° to 87.1°, PTSA changes from 6.3° to 5.5°. FCRA (femoral component coronal rotation angle) is 0.6° in A group, 0.4° in B group after operation. There were no significant difference between both groups (p > 0.05) (Table 2).

According to the clinical results, Knee score improved from 56.3 to 90.7, Functional score from 54.3 to 86.9 through operation in group A. In group B, Knee score improved from 54.9 to 89.8, Functional score from 52.8 to 84.6. The range of motion changes from 123.2° to 134.8° at group A and 122.5° to 133.4° at group B. There were no significant difference between both groups (p > 0.05) (Table 3).

Also a criteria for misalignment was set and postoperative femoral and tibial varus/valgus mismatch, posterior slope mismatch were assessed. The tibial varus/valgus mismatch cases after operation (nl.:87 ± 3°) was 1 in group A, 5 in group B. Post. slope mismatch cases after operation (nl.:7 ± 3°) was 1 in group A, 1 in group B. All cases in both A and B group were not included in femoral varus/valgus mismatch (nl.:0 ± 3°) after operation (Table 4). There were no significant difference between both groups on the radiologic or clinical results but cases with tibial varus/valgus mismatch in group A who used C-arm fluoroscope were relatively lesser than group B.

During follow up Complication happened at 2 cases, 1 case had polyethylene change because of abrasion of polyethylene, 1 case undergone total knee replacement because aseptic loosening of the implant occurred.

Also to assess the coincidence of the measurement of the images between different observers, Weighted kappa (κ) coefficient value was checked as 0.82 which means “almost perfect agreement”.

4 Discussion

For surgical treatment of degenerative arthritis of knee joint there are many methods such as arthroscopic surgery, femoral of tibial osteotomy, partial or total knee joint replacement and for each surgery various advantages and disadvantages, indications were reported.^4,10 For treatment of knee arthritis localized at the medial side, there are many reports of unicompartmental knee replacement arthroplasty. There are advantages such as lesser bleeding, minimize the extent of bone excision to reserve the bone structure so even though the unicompartmental knee replacement fails it is easy to change to total replacement.¹⁵ Also ACL and PCL, femoro-patellar joint are preserved to maintain stability of knee joint and early recovery so it is more used recently.^1,16,17

But there were limitations at the early times because of loosening, wearing and instability of the implant, mainly related to the failure of implant. Varus more than 5° of the proximal tibia, excessive varus/valgus of the femoral implant, valgus of the distal femur, excessive tibial slope were reported as the causes.^16,17 Kim et al.¹⁸ reported that deviation of the mechanical axis and FTA could be changed by the size of implant and polyethylene, the angle of tibial excision, the location of the femoral implant so they could effect the alignment after surgery. Weber et al.¹⁹ reported that certain increase of the tibial slope angle will reduce the abrasion of the implant, and by matching the alignment correctly complication such as implant failure can be reduced.

Recently techniques using navigation are used to maximize the accuracy of the alignment. Jung et al.²⁰ reported that unicompartmental knee replacement arthroplasty assisted by the navigation can enhance the accuracy of the femoral and tibial implant alignment on the sagittal plane. Seon et al.²¹ analyzed 31 cases using navigation during unicompartmental knee replacement and reported good results of alignment of lower extremities and implants. But due to disadvantages such as the more time and cost needed, the authors used C-arm fluoroscope and by using the accuracy of the alignment was increased and mismatch after tibial excision occurred less.

This study has limitations, it is a retrospective study, only assessed by radiologic and clinical results, risk of exposure of radiation, no assessment of the complications. But this study has a significance that C-arm fluoroscope is used during unicompartmental knee joint replacement and assessment of radiologic and clinical aspects of long term follow up are needed.

5 Conclusion

There was no statistically significant difference in radiologic and clinical results between group A and B, but the number of tibial varus/valgus mismatch case were fewer in fluoroscope guided group. So we consider that the fluoroscope is helpful for tibial cutting in unicompartmental knee replacement arthroplasty.

Conflict of interest

None.