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The Effect of Posterior Tibial Slope on Range of Motion After Total Knee Arthroplasty
The Journal of Arthroplasty Vol. 21 No. 6 2006
The Effect of Posterior Tibial Slope on Range of Motion After Total Knee Arthroplasty Devanshu Kansara, MD and David C. Markel, MD
Abstract: Posterior slope has been theorized as advantageous to range of motion (ROM) after total knee arthroplasty. This study was undertaken to assess the accuracy of a 08 and a 58 posterior sloped intramedullary (IM) cutting guide and the effect of the posterior tibial slope on postoperative ROM. Thirty-one consecutive patients underwent total knee arthroplasty using a cutting block and intramedullary cutting guide designed to impart a 08 posterior tibial slope (group 1). A 58 tibia cutting block was used in 30 subsequent patients (group 2). The posterior slope measurement represented the angle between a line drawn parallel to the articular surface and a line drawn perpendicular to the long axis of the tibia on a lateral radiograph. Mean postoperative tibial slope measured 1.88 for group 1 and 5.58 for group 2. There was no significant difference between groups for postoperative flexion or improvement of Hospital for Special Surgery score. The tibial cutting guides accurately achieved the intended posterior slope, but increasing posterior slope did not result in a significant increase in ROM or Hospital for Special Surgery functional score. Key words: posterior tibial slope, range of motion, Hospital for Special Surgery score, total knee arthroplasty. n 2006 Elsevier Inc. All rights reserved.
Several factors may affect the final postoperative ROM. These include the condition of the soft tissues (eg, flexion contracture, severe tibiofemoral varus or valgus), preoperative ROM, the surgical approach chosen, surgical technique, prosthetic geometry and size, preservation or substitution of the posterior cruciate ligament, the height of the joint line, prosthetic positioning, and the anteriorposterior tibial cut angle (tibial slope) [3 -11]. Most instrumentation systems used to perform a total knee arthroplasty allow the surgeon to adjust the angle of the proximal tibial cut in the sagittal plane. These instruments include fixed angle cutting blocks that are available in a variety of angles and cutting jigs that can be adjusted to a desired posterior inclination. Computer modeling indicates that increasing the posterior tibial tilt may increase postoperative ROM [4]. However, there have been no in vivo studies demonstrating the effects of the slope of the proximal tibial cut on ROM after total knee arthroplasty. There do not appear to be any data to confirm that tibial slope can be reliably altered by use of
Maximizing postoperative range of motion (ROM) is a desirable outcome of total knee arthroplasty. Increased motion is associated with improved function and increased patient satisfaction. Several studies [1,2] have demonstrated that patients require an average of 678 of flexion for the swing phase of gait, 838 to climb stairs, 908 to descend stairs, and 938 to rise from a seated position. In many countries in the Eastern hemisphere, flexion greater than 1058 is necessary for kneeling and squatting during activities of daily living and for religious acts [3].
From the Department of Orthopaedic Surgery, Wayne State University, Detroit, Michigan; and Department of Orthopaedic Surgery, Providence Hospital, Southfield, Michigan. Submitted June 30, 2004; revised , ; accepted August 14, 2005. Benefits or funds were received in partial or total support of the research material described in this article from OREF, Stryker, and Mid America Orthopaedic Foundation. Reprint requests: David C. Markel, MD, 22250 Providence Drive, Suite 401, Southfield, MI 48075. n 2006 Elsevier Inc. All rights reserved.
809
810 The Journal of Arthroplasty Vol. 21 No. 6 September 2006
Fig. 1. A, Schematic representation of the slope measurement method. A vertical line is drawn representing the longitudinal axis of the tibia. A horizontal line is drawn perpendicular to the vertical longitudinal. A third line is drawn along the superior margin of the proximal tibia representing its slope. The angle formed by the horizontal perpendicular and the proximal tibial margin represents the slope angle. B, Radiograph demonstrating the application of the measurement method outlined in panel A.
standard cutting guides. Theoretically, variation in the proximal tibial slope could be expected based on the style or type of cutting jig, jig stability, saw blade deflection, deviation in the surgeon’s hands, and others. This study assessed whether adjustment from a 08 cutting block to a 58 posterior sloped cutting block reliably reproduced the intended ostectomy angle. Secondly, the study assessed whether the increased posterior tibial slope led to increased postoperative ROM and improved function scores. We hypothesized that the cutting guide would accurately impart the desired slope to the proximal tibia and that increasing the posterior tibial slope would lead to an increase in the postoperative ROM.
Knee System (Scorpio Knee System; StrykerHowmedica-Osteonics, Allendale, NJ). All implants were of a posterior cruciate–sacrificing design, and the posterior cruciate ligament was excised in all cases. The only difference between groups was the use of a 08 or 58 posterior sloped tibial cutting block. The choice of cutting block angle was determined by the calendar year in which the index procedure took place. All procedures were performed by the senior author. The 58 consecutive total knee arthroplasties in 1998 used a 08-slope IM proximal tibial cutting block (Scorpio Knee System, StrykerHowmedica-Osteonics). These patients were designated group 1. In the following calendar year, 50 consecutive total knee arthroplasties were performed using a 58 posterior sloped cutting block. These patients were designated as group 2. Only primary knee arthroplasties were included. Patients were excluded if they carried a diagnosis of rheumatoid arthritis, previous osteotomy, or a requirement for a more constrained prosthetic design. Preoperative ROM and Hospital for Special Surgery (HSS) knee scores were prospectively obtained from each patient. Similar data were obtained for all patients at 3 months after surgery and at each patient’s most recent follow-up examination. Preoperative and postoperative radiographs of each surgical knee were obtained and measured to determine the tibial slope angle. All radiographs were previewed with stringent criteria for adequacy. Radiographic techniques that introduced obliquity in any plane were a cause for exclusion.
Materials and Methods The study population consisted of 108 consecutive knee arthroplasties performed on 101 consecutive patients who underwent primary total knee arthroplasty during the 2-year period (1998-1999). All of the procedures were performed through a medial parapatellar approach and used standard total knee arthroplasty instruments with intramedullary (IM) cutting guides from the Scorpio
Fig. 2. A, Radiograph demonstrating posterior slope, which is defined as the slope line proceeding from anterior-superior to posterior-inferior. Posterior slope is implied by a positive slope angle. B, Radiograph demonstrating anterior slope when the slope line proceeds from anterior-inferior to posterior-superior. Anterior slope is implied by a negative slope angle.
The Effect of Posterior Tibial Slope on Range of Motion After TKA ! Kansara and Markel 811 Table 1. Inclusion Groups Demographics Group 1
Group 2
Total
60 2 58 2 3 2 0 7 51 20 31
55 5 50 0 2 1 1 4 46 16 30
115 7 108 2 5 3 1 11 97 36 61
All arthroplasties Revision arthroplasties Primary arthroplasties Periprosthetic fractures Rheumatoid arthritis Hinged prosthesis Prior proximal tibial osteotomy Exclusions Arthroplasties included Unmeasureable radiographs Final groups
Images that did not contain enough of the tibial shaft to confidently determine the long axis of the tibia were excluded. Lateral radiographs of the knee were used to determine the long axis of the tibia. A line drawn perpendicular to the long axis of the tibia was defined as the reference line and represented 08 of slope. A line was then drawn parallel to the articular surface of the proximal tibia. The angle between the reference line and the articular surface line was designated the tibial slope angle (Fig. 1). If the slope proceeded from anterior-superior to posterior-inferior, it was designated a posterior slope and was assigned a positive value. If the posterior tibia had a higher elevation than the anterior tibia, then the slope was called an anterior slope and was given a negative value (Fig. 2). The data were analyzed with the SPSS statistical software package (SPSS, Inc, Chicago, Ill). A power analysis was performed to ensure that the study contained an adequate number of patients. The groups were compared using Student t test.
Results Five knees in 3 patients (4.3%) were excluded for a diagnosis of rheumatoid arthritis. Three patients
(2.6%) underwent arthroplasty with a hinged prosthesis and were excluded. One patient (0.8%) underwent revision surgery for a periprosthetic fracture, and another patient (0.8%) presented with a history of a prior distal femoral fracture that required open reduction and internal fixation. One patient had previously undergone a proximal tibial osteotomy. A total of 11 knees were excluded. Of the 97 knees that met inclusion criteria, 36 were excluded from the radiographic portion of the study because of radiographic technique that precluded radiographic measurement or not being able to meet stringent criteria to allow precise measurement. Of the 61 knees with measurable radiographs, 31 knees were in group 1 (08) and 30 knees were in group 2 (58) (Table 1). The mean of the preoperative proximal tibial slopes was 7.38 in group 1 (range, 08-138) and 7.78 in group 2 (range, 08-148). There was no statistically significant difference between the groups ( P = .182) before surgery. The mean preoperative knee extension was 3.28 in group 1 (range, 08-158) and 2.68 in group 2 (range, 08-108). Mean preoperative flexion was 101.18 in group 1 (range, 808-1308) and 99.38 in group 2 (range, 808-1408). The preoperative HSS score averaged 57.0 for group 1 (range, 20-82). Although the HSS score in group 2 was higher, averaging 62.0 (range, 39-80), the difference between the groups was not statistically significant ( P = .151). Use of the 08 cutting block in group 1 resulted in a mean postoperative proximal tibial slope of 1.88 (range, 48 to 98). This compared with the mean postoperative slope of 5.58 (range, 18-128) when cutting with the 58 jig in group 2 ( P = .2). Cutting with the 08 cutting block or the 58 cutting block did not result in a statistically significant difference in any of the outcome parameters measured, with the exception of extension. Although postoperative knee extension between groups at both time points tested was statistically different, the mean values differed by less
Table 2. Preoperative and Postoperative Group Comparisons Group 1 Preoperative proximal tibial slope Preoperative extension Preoperative flexion Preoperative HSS score Postoperative proximal tibial slope Postoperative extension Postoperative flexion Postoperative HSS score
7.38 3.28 101.18 57.0 1.88 0.28 123.38 81.9
(38 to 138) ( 158 to 08) (808 to 1308) (20 to 71) ( 48 to 98) (08 to 58) (908 to 1358) (63 to 98)
Group 2 7.78 2.68 99.38 62.0 5.58 0.08 119.68 78.2
(08 to 158) ( 158 to 08) (808 to 1408) (39 to 87) (18 to 128) ( 208 to 08) (758 to 1358) (51 to 99)
P b.001 .583 .703 .128 b.001 .323 .371 .223
812 The Journal of Arthroplasty Vol. 21 No. 6 September 2006 than 18. Table 2 summarizes the results and comparisons between the groups.
Discussion Many factors impact the ability to achieve maximum ROM after total knee arthroplasty. Some of these factors can be controlled by the surgeon. Others such as preoperative ROM cannot be controlled by the surgeon. Some authors have hypothesized that proximal tibial slope influences postoperative ROM. Walker and Garg [4], in a computer modeling study, attempted to determine the effect of proximal tibial slope on postoperative ROM. The effects of a 108 posterior tilt, neutral tilt, and a 108 anterior tilt were compared. He concluded that a 108 posterior tilt produced no less than 308 of additional flexion when compared with the neutral tilt and anterior tilt had the opposite effect. Although one could expect these results in a computer simulation, the model may have overlooked some very important anatomical and physiological variables. Clearly, the in vivo situation varies significantly from the analytical computer modeling because of confounding variables. This study used matched groups to evaluate the effect of slope on ROM and HSS score. This study used matched groups to evaluate the accuracy in achieving the intended slope of the tibial cut. Increasing the posterior slope by 58 did not affect postoperative ROM in a significant manner at either of the time points evaluated in this study. The variation in slope did not alter the clinical outcome as measured by the HSS knee scores. However, cutting the proximal tibia with the intent of creating a 08 slope had the deleterious radiographic outcome of an anterior slope in some patients. In contrast, attempting to impart a 58 posterior slope did not result in any patient having an anterior slope. This may be similar to the difficulty achieving and dangers associated with trying to impart a 38 varus cut in the tibia as in the early porous coated anatomic experience (Porous Coated Anatomic Knee; Howmedica, Rutherford, NJ) [12,13]. It may, therefore, be safer to use the 58 cutting blocks to eliminate the anterior slope variances. Measuring angles from plain radiographs has inherent error. The anterior bow of the tibia has the potential to introduce error into the determination of its longitudinal axis. Also, complicating measurement is the fact that most knee radiographs only include the proximal tibia. With these
considerations in mind, measurements were performed with the assumption that the longitudinal axis of the tibia would be represented by the path of an IM alignment rod. This path was estimated and used as the reference point upon which to base the perpendicular line that would represent a 08 slope. When studying radiographs, technique differences impose limitations on interpretation. To overcome this difficulty, our study went to great lengths to eliminate radiographs that were made at an oblique angle or did not include enough of the tibial diaphysis. The number of inadequate radiographs that were excluded may, at first glance, appear unacceptably high, but these exclusions were made to ensure accuracy and validity in the measurements [14]. In spite of these limitations, we believe that there is sufficient evidence to assert that an IM rod and a fixed angle cutting block can reproducibly impart a desired posterior slope cut. Small changes in proximal tibial slope did not have a significant impact on clinical outcome or ROM.
Conclusion Use of either a 08 or 58 proximal tibial cutting block and IM alignment jig accurately imparted the desired slope into a tibial cut. The variation in the cut did not appear to impact the outcome of the knee arthroplasty relative to ROM or knee function scores. The only variation noted was that, with the 58 cutting jigs, no tibial implants had an anterior slope after implantation. It may, therefore, be safer to use the 58 cutting blocks to eliminate the anterior slope variances.
References 1. Kettelkamp DB. Gait characteristics of the knee: normal, abnormal, and postreconstruction. American Academy of Orthopaedic Surgeons: symposium on Reconstructive Surgery of the Knee. St Louis: CV Mosby; 1976. p. 47. 2. Laubenthal KN, Smidt GL, Kettelkamp DB. A quantitative analysis of knee motion during activities of daily living. Phys Ther 1972;52:34. 3. Kim JM, Moon MS. Squatting following total knee arthroplasty. Clin Orthop 1995;313:177. 4. Walker PS, Garg A. Range of motion in total knee arthroplasty. A computer analysis. Clin Orthop 1991;262:227. 5. Ritter MA, Harty LD, Davis KE, et al. Predicting range of motion after total knee arthroplasty. J Bone Joint Surg Am 2003;85:1278.
The Effect of Posterior Tibial Slope on Range of Motion After TKA ! Kansara and Markel 813 6. Anouchi YS, McShane M, Kelly Jr F , et al. Range of motion in total knee replacement. Clin Orthop 1996; 331:87. 7. Mullen JO. Range of motion following total knee arthroplasty in ankylosed joints. Clin Orthop 1983; 179:200. 8. Parsley BS, Engh GA, Dwyer KA. Preoperative flexion. Does it influence post-operative flexion after posterior-cruciate–retaining total knee arthroplasty? Clin Orthop 1992;275:204. 9. Schurman DJ, Parker JN, Ornstein D. Total condylar knee replacement. A study of factors influencing range of motion as late as two years after arthroplasty. J Bone Joint Surg Am 1985; 67:1006.
10. Schurman DJ, Matityahu A, Goodman SB, et al. Prediction of postoperative knee flexion in InsallBurstein II total knee arthroplasty. Clin Orthop 1998;353:175. 11. Ritter MA, Stringer EA. Predictive range of motion after total knee replacement. Clin Orthop 1979; 143:115. 12. Ries MD. Endosteal referencing in revision total knee arthroplasty. J Arthroplasty 1998;13:85. 13. Ritter MA, Faris PM, Keating EM. Postoperative alignment of total knee replacement: its effect on survival. Clin Orthop 1994;299:153. 14. Lonner JL, Laird MT, Stuchin SA. Effect of rotation and knee flexion on radiographic alignment in total knee arthroplasties. Clin Orthop 1996;331:102.
The Effect of Posterior Tibial Slope on Range of Motion After Total Knee Arthroplasty Devanshu Kansara, MD and David C. Markel, MD
Abstract: Posterior slope has been theorized as advantageous to range of motion (ROM) after total knee arthroplasty. This study was undertaken to assess the accuracy of a 08 and a 58 posterior sloped intramedullary (IM) cutting guide and the effect of the posterior tibial slope on postoperative ROM. Thirty-one consecutive patients underwent total knee arthroplasty using a cutting block and intramedullary cutting guide designed to impart a 08 posterior tibial slope (group 1). A 58 tibia cutting block was used in 30 subsequent patients (group 2). The posterior slope measurement represented the angle between a line drawn parallel to the articular surface and a line drawn perpendicular to the long axis of the tibia on a lateral radiograph. Mean postoperative tibial slope measured 1.88 for group 1 and 5.58 for group 2. There was no significant difference between groups for postoperative flexion or improvement of Hospital for Special Surgery score. The tibial cutting guides accurately achieved the intended posterior slope, but increasing posterior slope did not result in a significant increase in ROM or Hospital for Special Surgery functional score. Key words: posterior tibial slope, range of motion, Hospital for Special Surgery score, total knee arthroplasty. n 2006 Elsevier Inc. All rights reserved.
Several factors may affect the final postoperative ROM. These include the condition of the soft tissues (eg, flexion contracture, severe tibiofemoral varus or valgus), preoperative ROM, the surgical approach chosen, surgical technique, prosthetic geometry and size, preservation or substitution of the posterior cruciate ligament, the height of the joint line, prosthetic positioning, and the anteriorposterior tibial cut angle (tibial slope) [3 -11]. Most instrumentation systems used to perform a total knee arthroplasty allow the surgeon to adjust the angle of the proximal tibial cut in the sagittal plane. These instruments include fixed angle cutting blocks that are available in a variety of angles and cutting jigs that can be adjusted to a desired posterior inclination. Computer modeling indicates that increasing the posterior tibial tilt may increase postoperative ROM [4]. However, there have been no in vivo studies demonstrating the effects of the slope of the proximal tibial cut on ROM after total knee arthroplasty. There do not appear to be any data to confirm that tibial slope can be reliably altered by use of
Maximizing postoperative range of motion (ROM) is a desirable outcome of total knee arthroplasty. Increased motion is associated with improved function and increased patient satisfaction. Several studies [1,2] have demonstrated that patients require an average of 678 of flexion for the swing phase of gait, 838 to climb stairs, 908 to descend stairs, and 938 to rise from a seated position. In many countries in the Eastern hemisphere, flexion greater than 1058 is necessary for kneeling and squatting during activities of daily living and for religious acts [3].
From the Department of Orthopaedic Surgery, Wayne State University, Detroit, Michigan; and Department of Orthopaedic Surgery, Providence Hospital, Southfield, Michigan. Submitted June 30, 2004; revised , ; accepted August 14, 2005. Benefits or funds were received in partial or total support of the research material described in this article from OREF, Stryker, and Mid America Orthopaedic Foundation. Reprint requests: David C. Markel, MD, 22250 Providence Drive, Suite 401, Southfield, MI 48075. n 2006 Elsevier Inc. All rights reserved.
809
810 The Journal of Arthroplasty Vol. 21 No. 6 September 2006
Fig. 1. A, Schematic representation of the slope measurement method. A vertical line is drawn representing the longitudinal axis of the tibia. A horizontal line is drawn perpendicular to the vertical longitudinal. A third line is drawn along the superior margin of the proximal tibia representing its slope. The angle formed by the horizontal perpendicular and the proximal tibial margin represents the slope angle. B, Radiograph demonstrating the application of the measurement method outlined in panel A.
standard cutting guides. Theoretically, variation in the proximal tibial slope could be expected based on the style or type of cutting jig, jig stability, saw blade deflection, deviation in the surgeon’s hands, and others. This study assessed whether adjustment from a 08 cutting block to a 58 posterior sloped cutting block reliably reproduced the intended ostectomy angle. Secondly, the study assessed whether the increased posterior tibial slope led to increased postoperative ROM and improved function scores. We hypothesized that the cutting guide would accurately impart the desired slope to the proximal tibia and that increasing the posterior tibial slope would lead to an increase in the postoperative ROM.
Knee System (Scorpio Knee System; StrykerHowmedica-Osteonics, Allendale, NJ). All implants were of a posterior cruciate–sacrificing design, and the posterior cruciate ligament was excised in all cases. The only difference between groups was the use of a 08 or 58 posterior sloped tibial cutting block. The choice of cutting block angle was determined by the calendar year in which the index procedure took place. All procedures were performed by the senior author. The 58 consecutive total knee arthroplasties in 1998 used a 08-slope IM proximal tibial cutting block (Scorpio Knee System, StrykerHowmedica-Osteonics). These patients were designated group 1. In the following calendar year, 50 consecutive total knee arthroplasties were performed using a 58 posterior sloped cutting block. These patients were designated as group 2. Only primary knee arthroplasties were included. Patients were excluded if they carried a diagnosis of rheumatoid arthritis, previous osteotomy, or a requirement for a more constrained prosthetic design. Preoperative ROM and Hospital for Special Surgery (HSS) knee scores were prospectively obtained from each patient. Similar data were obtained for all patients at 3 months after surgery and at each patient’s most recent follow-up examination. Preoperative and postoperative radiographs of each surgical knee were obtained and measured to determine the tibial slope angle. All radiographs were previewed with stringent criteria for adequacy. Radiographic techniques that introduced obliquity in any plane were a cause for exclusion.
Materials and Methods The study population consisted of 108 consecutive knee arthroplasties performed on 101 consecutive patients who underwent primary total knee arthroplasty during the 2-year period (1998-1999). All of the procedures were performed through a medial parapatellar approach and used standard total knee arthroplasty instruments with intramedullary (IM) cutting guides from the Scorpio
Fig. 2. A, Radiograph demonstrating posterior slope, which is defined as the slope line proceeding from anterior-superior to posterior-inferior. Posterior slope is implied by a positive slope angle. B, Radiograph demonstrating anterior slope when the slope line proceeds from anterior-inferior to posterior-superior. Anterior slope is implied by a negative slope angle.
The Effect of Posterior Tibial Slope on Range of Motion After TKA ! Kansara and Markel 811 Table 1. Inclusion Groups Demographics Group 1
Group 2
Total
60 2 58 2 3 2 0 7 51 20 31
55 5 50 0 2 1 1 4 46 16 30
115 7 108 2 5 3 1 11 97 36 61
All arthroplasties Revision arthroplasties Primary arthroplasties Periprosthetic fractures Rheumatoid arthritis Hinged prosthesis Prior proximal tibial osteotomy Exclusions Arthroplasties included Unmeasureable radiographs Final groups
Images that did not contain enough of the tibial shaft to confidently determine the long axis of the tibia were excluded. Lateral radiographs of the knee were used to determine the long axis of the tibia. A line drawn perpendicular to the long axis of the tibia was defined as the reference line and represented 08 of slope. A line was then drawn parallel to the articular surface of the proximal tibia. The angle between the reference line and the articular surface line was designated the tibial slope angle (Fig. 1). If the slope proceeded from anterior-superior to posterior-inferior, it was designated a posterior slope and was assigned a positive value. If the posterior tibia had a higher elevation than the anterior tibia, then the slope was called an anterior slope and was given a negative value (Fig. 2). The data were analyzed with the SPSS statistical software package (SPSS, Inc, Chicago, Ill). A power analysis was performed to ensure that the study contained an adequate number of patients. The groups were compared using Student t test.
Results Five knees in 3 patients (4.3%) were excluded for a diagnosis of rheumatoid arthritis. Three patients
(2.6%) underwent arthroplasty with a hinged prosthesis and were excluded. One patient (0.8%) underwent revision surgery for a periprosthetic fracture, and another patient (0.8%) presented with a history of a prior distal femoral fracture that required open reduction and internal fixation. One patient had previously undergone a proximal tibial osteotomy. A total of 11 knees were excluded. Of the 97 knees that met inclusion criteria, 36 were excluded from the radiographic portion of the study because of radiographic technique that precluded radiographic measurement or not being able to meet stringent criteria to allow precise measurement. Of the 61 knees with measurable radiographs, 31 knees were in group 1 (08) and 30 knees were in group 2 (58) (Table 1). The mean of the preoperative proximal tibial slopes was 7.38 in group 1 (range, 08-138) and 7.78 in group 2 (range, 08-148). There was no statistically significant difference between the groups ( P = .182) before surgery. The mean preoperative knee extension was 3.28 in group 1 (range, 08-158) and 2.68 in group 2 (range, 08-108). Mean preoperative flexion was 101.18 in group 1 (range, 808-1308) and 99.38 in group 2 (range, 808-1408). The preoperative HSS score averaged 57.0 for group 1 (range, 20-82). Although the HSS score in group 2 was higher, averaging 62.0 (range, 39-80), the difference between the groups was not statistically significant ( P = .151). Use of the 08 cutting block in group 1 resulted in a mean postoperative proximal tibial slope of 1.88 (range, 48 to 98). This compared with the mean postoperative slope of 5.58 (range, 18-128) when cutting with the 58 jig in group 2 ( P = .2). Cutting with the 08 cutting block or the 58 cutting block did not result in a statistically significant difference in any of the outcome parameters measured, with the exception of extension. Although postoperative knee extension between groups at both time points tested was statistically different, the mean values differed by less
Table 2. Preoperative and Postoperative Group Comparisons Group 1 Preoperative proximal tibial slope Preoperative extension Preoperative flexion Preoperative HSS score Postoperative proximal tibial slope Postoperative extension Postoperative flexion Postoperative HSS score
7.38 3.28 101.18 57.0 1.88 0.28 123.38 81.9
(38 to 138) ( 158 to 08) (808 to 1308) (20 to 71) ( 48 to 98) (08 to 58) (908 to 1358) (63 to 98)
Group 2 7.78 2.68 99.38 62.0 5.58 0.08 119.68 78.2
(08 to 158) ( 158 to 08) (808 to 1408) (39 to 87) (18 to 128) ( 208 to 08) (758 to 1358) (51 to 99)
P b.001 .583 .703 .128 b.001 .323 .371 .223
812 The Journal of Arthroplasty Vol. 21 No. 6 September 2006 than 18. Table 2 summarizes the results and comparisons between the groups.
Discussion Many factors impact the ability to achieve maximum ROM after total knee arthroplasty. Some of these factors can be controlled by the surgeon. Others such as preoperative ROM cannot be controlled by the surgeon. Some authors have hypothesized that proximal tibial slope influences postoperative ROM. Walker and Garg [4], in a computer modeling study, attempted to determine the effect of proximal tibial slope on postoperative ROM. The effects of a 108 posterior tilt, neutral tilt, and a 108 anterior tilt were compared. He concluded that a 108 posterior tilt produced no less than 308 of additional flexion when compared with the neutral tilt and anterior tilt had the opposite effect. Although one could expect these results in a computer simulation, the model may have overlooked some very important anatomical and physiological variables. Clearly, the in vivo situation varies significantly from the analytical computer modeling because of confounding variables. This study used matched groups to evaluate the effect of slope on ROM and HSS score. This study used matched groups to evaluate the accuracy in achieving the intended slope of the tibial cut. Increasing the posterior slope by 58 did not affect postoperative ROM in a significant manner at either of the time points evaluated in this study. The variation in slope did not alter the clinical outcome as measured by the HSS knee scores. However, cutting the proximal tibia with the intent of creating a 08 slope had the deleterious radiographic outcome of an anterior slope in some patients. In contrast, attempting to impart a 58 posterior slope did not result in any patient having an anterior slope. This may be similar to the difficulty achieving and dangers associated with trying to impart a 38 varus cut in the tibia as in the early porous coated anatomic experience (Porous Coated Anatomic Knee; Howmedica, Rutherford, NJ) [12,13]. It may, therefore, be safer to use the 58 cutting blocks to eliminate the anterior slope variances. Measuring angles from plain radiographs has inherent error. The anterior bow of the tibia has the potential to introduce error into the determination of its longitudinal axis. Also, complicating measurement is the fact that most knee radiographs only include the proximal tibia. With these
considerations in mind, measurements were performed with the assumption that the longitudinal axis of the tibia would be represented by the path of an IM alignment rod. This path was estimated and used as the reference point upon which to base the perpendicular line that would represent a 08 slope. When studying radiographs, technique differences impose limitations on interpretation. To overcome this difficulty, our study went to great lengths to eliminate radiographs that were made at an oblique angle or did not include enough of the tibial diaphysis. The number of inadequate radiographs that were excluded may, at first glance, appear unacceptably high, but these exclusions were made to ensure accuracy and validity in the measurements [14]. In spite of these limitations, we believe that there is sufficient evidence to assert that an IM rod and a fixed angle cutting block can reproducibly impart a desired posterior slope cut. Small changes in proximal tibial slope did not have a significant impact on clinical outcome or ROM.
Conclusion Use of either a 08 or 58 proximal tibial cutting block and IM alignment jig accurately imparted the desired slope into a tibial cut. The variation in the cut did not appear to impact the outcome of the knee arthroplasty relative to ROM or knee function scores. The only variation noted was that, with the 58 cutting jigs, no tibial implants had an anterior slope after implantation. It may, therefore, be safer to use the 58 cutting blocks to eliminate the anterior slope variances.
References 1. Kettelkamp DB. Gait characteristics of the knee: normal, abnormal, and postreconstruction. American Academy of Orthopaedic Surgeons: symposium on Reconstructive Surgery of the Knee. St Louis: CV Mosby; 1976. p. 47. 2. Laubenthal KN, Smidt GL, Kettelkamp DB. A quantitative analysis of knee motion during activities of daily living. Phys Ther 1972;52:34. 3. Kim JM, Moon MS. Squatting following total knee arthroplasty. Clin Orthop 1995;313:177. 4. Walker PS, Garg A. Range of motion in total knee arthroplasty. A computer analysis. Clin Orthop 1991;262:227. 5. Ritter MA, Harty LD, Davis KE, et al. Predicting range of motion after total knee arthroplasty. J Bone Joint Surg Am 2003;85:1278.
The Effect of Posterior Tibial Slope on Range of Motion After TKA ! Kansara and Markel 813 6. Anouchi YS, McShane M, Kelly Jr F , et al. Range of motion in total knee replacement. Clin Orthop 1996; 331:87. 7. Mullen JO. Range of motion following total knee arthroplasty in ankylosed joints. Clin Orthop 1983; 179:200. 8. Parsley BS, Engh GA, Dwyer KA. Preoperative flexion. Does it influence post-operative flexion after posterior-cruciate–retaining total knee arthroplasty? Clin Orthop 1992;275:204. 9. Schurman DJ, Parker JN, Ornstein D. Total condylar knee replacement. A study of factors influencing range of motion as late as two years after arthroplasty. J Bone Joint Surg Am 1985; 67:1006.
10. Schurman DJ, Matityahu A, Goodman SB, et al. Prediction of postoperative knee flexion in InsallBurstein II total knee arthroplasty. Clin Orthop 1998;353:175. 11. Ritter MA, Stringer EA. Predictive range of motion after total knee replacement. Clin Orthop 1979; 143:115. 12. Ries MD. Endosteal referencing in revision total knee arthroplasty. J Arthroplasty 1998;13:85. 13. Ritter MA, Faris PM, Keating EM. Postoperative alignment of total knee replacement: its effect on survival. Clin Orthop 1994;299:153. 14. Lonner JL, Laird MT, Stuchin SA. Effect of rotation and knee flexion on radiographic alignment in total knee arthroplasties. Clin Orthop 1996;331:102.