Biomaterials 20 (1999) 85 — 89

Morsellized bone grafting compensates for femoral bone loss in revision total knee arthroplasty. An experimental study C.J.M. van Loon, M.C. de Waal Malefijt*, N. Verdonschot, P. Buma, A.J.A.M. van der Aa, R. Huiskes Orthopaedic Research Laboratory, Department of Orthopaedics, University of Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands Received 12 February 1998; accepted 25 June 1998

Abstract This study was undertaken to examine the contribution of uncontained morsellized bone graft to the structural properties of a femoral reconstruction in total knee arthroplasty and to serve as a basis for an in vivo animal study. Ten human distal femora with a standard unicondylar uncontained medial bone defect were prepared to fit a femoral component of a cruciate sacrificing TKA. A cyclic axial load of 750 N was applied to the medial part of the femoral component in the presence of impacted morsellized bone graft. After removal of the bone graft, the cyclic loading was repeated for the unsupported situation. None of the grafts collapsed and all cement mantles stayed intact during the experiments. Elastic deformation during cyclic loading was significantly less when graft was added while time-dependent deformation was not affected. We conclude that impacted morsellized bone graft, used for reconstruction of uncontained femoral bone loss in revision knee arthroplasty, may improve the structural resistence against loading. Further animal experimentation for in vivo application is warranted.  1998 Published by Elsevier Science Ltd. All rights reserved Keywords: Total knee arthroplasty; Morsellized bone graft; Revision; Bone defect

1. Introduction Uncontained femoral bone loss is often encountered in revision total knee arthroplasty (TKA) due to bone remodeling, wear and removal of the implant [1—3]. Massive bone graft, cement and metal augmentation have been used to reconstruct these defects. Massive bone grafts are liable to clinical failure [4]. In view of the very good long-term results of impacted morsellized bone grafts in revision total hip arthroplasty (THA) [5], we propose impacted morsellized bone grafting for femoral bone defects in combination with a cemented TKA. Unlike revision THA, however, femoral bone defects in revision TKA are often uncontained, creating the problem of lack of support. In cases of uncontained acetabular and femoral bone loss in THA, metal meshes are often used to create containment for the impacted morsellized bone graft. These meshes are less applicable in TKA, since the mandatory soft tissue coverage is often absent or insufficient. Hence, the morsellized bone graft may collapse under loading conditions. * Corresponding author. Tel.: 0031 24 3613918; fax: 0031 24 3540230.

The present study was undertaken to examine the contribution of the uncontained morsellized graft to the structural properties of the reconstruction and to serve as a basis for an in vivo animal study. For this purpose, the stiffness of the reconstruction and the deformational behavior with and without grafts under cyclic loading was measured.

2. Materials and methods Ten fresh frozen human distal femoral bones were prepared to fit the femoral component of a cruciate sacrificing TKA (Press-Fit Condylar, Johnson and Johnson, Raynham, MA, USA). After trial fitting of the component, a standard uncontained unicondylar bone defect was created by removing 1 cm of the distal medial condyle. The defect was reconstructed with morsellized bone graft, manually impacted in a mould (Fig. 1). After removal of the mould the femoral component was cemented on the distal femur with the graft in place. The proximal end of the femoral shaft was potted in cement and clamped in an upside down position in a testing

0142-9612/98/$—See front matter  1998 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 6 1 2 ( 9 8 ) 0 0 1 5 5 - 0

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Fig. 1. Distal femoral cadaveric bone in an upside down position after preparation for a femoral component and creation of an uncontained unicondylar bone defect. Morsellized bone graft is impacted into the defect with a perfect loose-fit mould in position.

machine (MTS, model 458020, Systems Corporation Minneapolis Minnesota). Zero measurements without loading were performed during 152 s. A cyclic axial load ranging from zero to 750 N with a 1 Hz frequency was then applied to the medial part of the femoral component (without a tibial component) for approximately one hour (3321 cycles, test A, Fig. 2). The loading peg had freedom of movement in the anterior/posterior and medial/lateral directions during axial loading. The same test was repeated after manual removal of the impacted graft to create a situation where no graft support for the femoral component was present (test B, Fig. 3). Graft collapse or cement failure was monitored by measuring the elastic and time-dependent deformation between prosthesis and bone at the medial and lateral side by two extensometers, with a resolution of 8 lm. The extensometers were aligned in the axial direction, where maximal deformations were expected. Elastic deformation was defined as the local displacement between the distal femur and the prosthesis, measured by the extensometers, during each loading cycle. Hence, elastic deformation may include bony deformation and displacement at the interfaces. Time-dependent deformation was defined as the ungoing change in local displacement, measured by the extensometers in time. Statistical analysis of the test data was performed with the paired Wilcoxon signed rank test, comparing the difference in elastic and time-dependent deformation for tests A and B. P-values less than 0.05 were considered significant.

Fig. 2. Experimental set-up of a distal femoral cadaver bone, in an upside down position, with a cemented femoral component and impacted morsellized bone graft. Two extensometers (resolution: 8 lm) are placed at the medial and lateral condyles to measure elastic and time-dependent deformation. A cyclic axial loading of 750 N is applied at the medial part of the prosthesis through a peg.

Fig. 3. Distal femoral cadaveric bone with a cemented femoral component after removal of the morsellized bone graft.

3. Results Cyclic deformation between distal femur and prosthesis was observed in tests A and B. None of the impacted morsellized grafts collapsed during the loading experi-

ments. All cement mantles remained intact on visual inspection during and after the tests. Elastic and timedependent deformations differed considerably from specimen to specimen (Figs. 4 and 5, Tables 1 and 2). Hence,

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Fig. 4. Elastic deformation between the distal femur and the femoral component at the medial condyle in the presence (test A) and absence (test B) of impacted morsellized bone graft (10 cases). The error bars represent the standard deviation. The elastic deformation was measured by an extensometer at the medial condyle (resolution: 8 lm).

Fig. 5. Time-dependent deformation between the distal femur and the femoral component at the medial condyle in the presence (test A) and absence (test B) of impacted morsellized bone graft (10 cases). The error bars represent the standard deviation. The time-dependent deformation was measured by an extensometer at the medial condyle (resolution: 8.1 lm).

the inter-specimen variation was rather high. However, the intra-specimen results, analyzing purely the effect of the presence of the graft material in a particular specimen, indicated a significant effect of the presence of the graft on the stability of the reconstruction. The elastic deformation between the cement and the bone measured in test A was significantly less at the medial (Fig. 4, P"0.002) and lateral (P"0.0039) condyles, when compared to test B. The differences in time-dependent deformation between tests A and B were not significant for the

medial (Fig. 5, P"0.7) or lateral (P"0.63) condyles. Time-dependent measurements at the lateral condyle gave negative values, indicating that the prosthesis was subject to tilting.

4. Discussion The treatment of bone loss in revision TKA is a challenge. Surgeons often underestimate the amount of

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Table 1 Values of elastic deformation (micron) at the medial condyle of 10 distal femora with cemented femoral components in the presence (test A) and absence (test B) of impacted morsellized bonegraft after 3321 cycles of axial loading with 750 N. The elastic deformation was measured by an extensometer at the medial condyle (resolution: 8 lm) Specimen

Test A

Test B

1 2 3 4 5 6 7 8 9 10 Mean Standard deviation

527 404 877 878 656 554 410 975 540 697 652 202

739 702 1205 1035 898 958 428 1153 642 749 851 243

Table 2 Values of time-dependent deformation (micron) at the medial condyle of 10 distal femora with cemented femoral components in the presence (test A) and absence (test B) of impacted morsellized bonegraft after 3321 cycles of axial loading with 750 N. The time-dependent deforma tion was measured by an extensometer at the medial condyle (resolution: 8 lm) Specimen

femoral bone loss preoperatively, and may be surprised by large defects that require reconstruction [3, 6]. In the case of uncontained femoral bone loss, Engh et al. [7] recommended the use of a stemmed femoral component to protect structural grafts. However, the application of a femoral stem extension may lead to increased femoral bone resorption, due to the stress shielding effect of the stem [8]. Therefore, a solution to uncontained femoral bone loss without a stemmed component seems advantageous. The present study addressed the question whether impacted morsellized bone graft, used in cemented revision TKA with unicondylar uncontained femoral bone loss, would remain stable and would contribute to reduction of elastic and time-dependent deformation under the loading conditions, comparable to a patient’s full body weight. This unicondylar load of the grafted condyle in cadaver bones exceeded the clinical situation. Both femoral condyles normally share the patient’s body-weight when post-operative alignment is correct. A delay in full weightbearing of about 3 months is commonly advised in revision TKA with bone grafting, untill the graft is incorporated. Our results show that collapse of the impacted morsellized bone graft does not occur under the present loading conditions. The support from the intact lateral condyle, the inter-condylar box and the impacted morsellized bone graft to the cemented femoral component is adequate to prevent early mechanical failure. Our results showed similar patterns for elastic deformation for all femora at the end of the test. The highstandard deviations in the values of the deformations were caused by differences in individual bone quality and geometry of the cadaver specimens. Elastic deformations, an indicator for strength, at the medial and lateral condyles were about 20% less in test A. Although this did

1 2 3 4 5 6 7 8 9 10 Mean Standard deviation

Test A 276 264 750 800 494 282 !60 177 177 262 342 266

Test B 268 269 1397 443 389 305 26 231 23 138 349 393

not suggest a dramatic increase in stability, the paired differences were significant. This implies that reconstruction with impacted morsellized bone graft does reduce deformation to some extent. The lack of reduction in time-dependent deformation from tests A—B, however, remains a matter of concern. The absence of cortical support may cause early failure of the reconstruction of large bone defects if direct postoperative loading with full body weight is allowed. Our study only simulates the direct post-operative situation and does not investigate stability during the bone remodeling process. However, initial laboratory tests are essential in the process of stepwise introduction of new implant fixation methods, to monitor safety and efficacy [9]. By offering a scaffold for bone ingrowth, this technique may enable restoration of bone mass in the longer term. Further mechanical and biological tests of this new method will be conducted in an animal experiment. We conclude that impacted morsellized bone graft used for uncontained unicondylar femoral bone defects in in vivo cemented TKA may not collapse under dynamic loading. The structural resistence against load may be improved relative to the unsupported situation, although time-dependent deformation is not reduced.

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C.J.M. van Loon et al. / Biomaterials 20 (1999) 85—89 [3] Robinson EJ, Mulliken BD, Bourne RB, Rorabeck CH, Alvarez C. Catastrophic osteolysis in total knee replacement. Clin Orthop 1995;321:98—105. [4] Waal Malefijt MC de, Kampen A van, Slooff TJJH. Bone grafting in cemented knee replacement; 45 primary and secondary cases followed for 2—5 years. Acta Orthop Scand 1995;66:325—32. [5] Schreurs BW, Slooff TJJH, Buma P, Gardeniers JWM, Huiskes R. Acetabular reconstruction with impacted morsellised cancellous bone graft and cement. Jt Bone J Surg 1998;80-B:391—5. [6] Elia EA, Lotke PA. Results of revision total knee arthroplasty associated with significant bone loss. Clin Orthop 1991; 271:114—21.

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[7] Engh GA, Herzwurm PJ, Parks NL. Treatment of major defects of bone with bulk allografts and stemmed components during knee arthroplasty. J Bone Jt Surg 1997;79-A:1030—9. [8] Willems MMM, Lenthe GH van, Verdonschot N, de Waal Malefijt MC, Huiskes R. Fixation methods of a stemmed femoral component of a total knee replacement strongly influence eventual bone loss. Transactions of 8th EORS Annual Meeting. Amsterdam, 1998:51. [9] Huiskes R. Failed innovation in total hip replacement. Diagnosis and proposals for a cure. Acta Orthop Scand 1993; 64:699—716.