Osteotomy of the tibial tubercle (TT) was suggested to improve exposure during knee surgery  and is used in total knee arthroplasty (TKA) when stiffness precludes appropriate eversion of the patella, whether it be related to primary disease or fibrosis in revision cases. This is undertaken even more readily when the patella is low or malaligned; repositioning the tuberosity improves the patellar index.
The objectives of this study were to verify the feasibility of tubercle displacement and to describe any complications as well as to describe the relation between tubercle translation and patellar index improvement. Our hypothesis was that osteotomy of the TT with an anteromedial approach would remove the risk of patellar tendon rupture, that it could be done reproducibly, and that it would contribute to improving knee function in cases of patella baja.
This article will not discuss TT osteotomy with an anterolateral approach in which the technical basis is similar, with the hinge represented by the medial periosteum ), performed systematically [3, 4] or out of necessity [5, 6].
Patients and methods
From 1993 to 2006, 21 TT osteotomies were performed in 20 patients (10 males and 10 females) with a mean age of 71 years (range, 42–90 years) and a mean BMI of 25.5±2.9kg/m2 (range, 21–32kg/m2). During this period, 510 total knee arthroplasties were performed, 58 of which were revisions. The revisions were all performed via the anteromedial approach, as were 90% of the primary implantations. Seven cases involved a primary arthroplasty on stiff knees, two of which were after osteotomy and one after clearing the joint of septic osteoarthritis. Fourteen cases involved prosthetic revision (12 first revisions, two second revisions): 11 for aseptic loosening and three for septic loosening, with the exchange done in two steps and the TT translation always performed in the second surgical session during prosthesis reimplantation.
The indication for TT dislocation was selected for stiff knees in which the risk of patellar tendon rupture seemed substantial or with preoperative or predictable patella baja (e.g., exchanging a tibial insert for a thicker one) (Figure 1). Osteolysis was not a criterion for exclusion (Figure 2), but there was no massive osteolysis in the series.
Multioperated knee: 1997, TKA; 2007, femoral fracture with retrograde nailing. Medial+lateral laxity+recurvatum; 2008, insert exchange (from 12 to 20 mm thick); TT translation, 15 mm.Zoom
Case no. 2. Tibial plate rupture due to osteolysis. Defect packed with bone substitute. TT translation, 13 mm. Resorbable screws. 7years follow-up. ROM, 0/0/100°; patellar index improved from 0.12 to 0.23.Zoom
The description of the total series is presented in Table 1.
The operation was performed without a pneumatic tourniquet in all cases. For a knee that had already been operated, the original cutaneous incision was used and then in deeper tissues an anteromedial parapatellar approach between the rectus femoris muscle and the vastus medialis proximally and extended distally for approximately 10 cm below the TT. The distal line of the osteotomy was cut first with the oscillating saw between two small drill holes; then the frontal cut was made with a chisel (from medial to lateral; Figure 3). The bone flap had to be at least 1 cm thick and 7 cm long. Levering the bone fragment on the lateral musculoperiosteal hinge then gave excellent visualization of the joint. At the end of the intervention, releasing the lateral periosteum might be necessary to mobilize the bone fragment, but the muscle attachments had to be kept intact. Fixation was ensured either in situ (two cases) or by modifying the position in medial or proximal translation (proximal, 19 cases). The transversal aspect of the distal osteotomy cut made it possible to use a distractor if the TT translation was difficult. The translation was limited by the distraction force or the upper edge of the fragment in relation with the prosthetic tibial baseplate. Fixation was provided by two compression screws (Figure 4) going one side or the other of a keel or prosthetic intramedullary stem. Initially, the screws were metallic (the same alloy as that used for the tibial plate) (Figure 5). Since 1995, we have used resorbable screws in polylactic acid (Phusis, Saint Ismier, France) initially with a round head (which required reaming in the TT). Since 2000, we have used a model with a flat head designed specifically for tubercle transpositions (Phusis). The material disappears progressively by hydrolysis .
Distal step-cut osteotomy, proximal sloping, coronal from medial to lateral. Levering the fragment on its lateral hinge.Zoom
Fixation with two resorbable screws. Measuring tibial tubercle translation (double arrow).Zoom
Case no. 13. Stiff knee after tuberculosis (−10°/10). 1994, TT osteotomy necessary to expose for the TKA. Two metallic screws. Judet quadriceps release at 6weeks (the fixation was reliable). At 10years, ROM, 0/0/80°; patellar index, initially 0.23, 0.28 at follow-up.Zoom
The recovery period was conducted in the same way as for an implant without osteotomy: the knee at rest in a brace in extension, posture in extension, isometric work on the quadriceps, and spontaneous recovery of flexion. Preoperative stiffness did not alter the rehabilitation. Weightbearing was immediate for primary implant patients and differed for 3 weeks in prosthesis changes (determined by bone reconstruction).
The patients were seen regularly (2 months, 6 months, 1 year, then every 2 years) with a mean follow-up of 54 months±47.8. We used the IKS score. Radiologically, we assessed the condition of the fragment (union, position) and patellar height using the index described by Jacquot  during the 1999 Lyon Knee Days (Figure 6). This index has the advantage of not depending on the knee flexion angle, size or position of the patellar implant, length of the patellar tendon, tibial slope, or radiological enlargement. It has the disadvantage of lacking a published reference value.
Patellar index (I/P) without prosthesis (left) and with a TKA (right).Zoom
The statistical analysis was performed using the Mann-Whitney test.
We analyzed the results of the entire series, then the “revision TKA” and “primary TKA” subgroups.
Some complications were nonspecific of the tubercle osteotomy. One case of prepatellar partial cutaneous necrosis (5cm2) on a knee having undergone several interventions healed by secondary healing. Stiffness (0/0/50°) did not seem to be related to the TT osteotomy but had substantial pre- and postoperative trophic impairment with the soft tissues highly infiltrated. A traumatic fracture of the tibia with an intramedullary stem, slightly displaced (underlying the osteotomy zone) healed with a long-leg cast. However, we observed two cases of a complication specific to the TT translation: a stress fracture of the proximal extremity of the bone fragment extending beyond the metallic tibial tray (Figure 7). Rest led to bone union and the disappearance of pain in 2 months.
Case no. 19. Overhang of the proximal part of TT. Fatigue fracture healed with relative rest.Zoom
Results of the overall series
The mean preoperative total IKS score was 100±33.9 (range, 25–168), with the knee score at 57.5±22.4 (range, 5–88) and the function score at 42.6±21.5 (range, −10 to 80). At 54 months follow-up, the mean total score was 149±32.9 (range, 73–194), with the knee score at 84±11.6 (range, 43–95). The mean preoperative flexion was 78.8° (range, 0–120; standard deviation [SD], 36), at follow-up 88.6° (range, 40–120; SD, 21.9) for a mean gain in flexion of 9.8° (range, −20° to 80°; SD, 24.2). The mean extension angle decreased from 4°±7.3 (range, −10° to 20°) to 0.7°±2.2 (range, 0–10) for a gain in extension of 4°±7.2 (−5° to 20°). The joint range of motion increased from 73°±34.9 (range, 10°–120°) to 88°±21.1 (range, 30°–120°) at the follow-up, for a mean gain of 15°±23.6 (Table 2).
We observed no malunion, necrosis, or secondary migration of the bone fragment, which showed union in a mean 3.5 months±1.6 (range, 1–6 months). The mean translation in the 19 cases in which the TT was displaced (Figure 4) was 13 mm±6 (range, 8–33 mm). The preoperative patellar index increased from 0.18±0.20 (range, −0.39 to 0.57) to 0.33±0.19 (range, −0.13 to 0.60) at follow-up, for a gain of 0.15±0.78; there was no modification in the patellar index value between the immediate postoperative measurement and the follow-up measurement.
“Primary” and “revision” subgroup results
The increase in clinical capacities and the gain in the patellar index were higher in the primary arthroplasty subgroup than in the TKA revision subgroup [p (IKS gain)=0.26; p (extension gain)=0.20; p (flexion gain)=0.43; p (IP gain)=0.76] (Table 3, Table 4).
ATT osteotomy is a rare indication (approximately 5% of the cases operated in the same period) during knee arthroplasty, but it facilitates the anteromedial approach in a stiff joint and allows modification of the patellar position by acting on the distal side of the extensor system.
The major risk
The major risk during the approach, in which sufficient patellar eversion is necessary for good exposure, is detachment of the patellar tendon from its tibial insertion, as highlighted by Bellemans  and Rand et al. , which can lead to an active extension lag and difficult locking of the knee, a difficult handicap to control.
The extensor system
The extensor system can be released distally (TT) or proximally. In 1943, Coonse and Adams  described the turndown of the patellar tendon-patella-quadriceps tendon group toward the front, with the proximal V sutured in a Y  to lengthen the extensor apparatus proximally. In 1984, Insall  modified these concepts by starting from a medial approach rising between the rectus femoris muscle and the vastus medialis to descend diagonally toward the superolateral angle of the patella. This quadriceps turndown levels the distal part of the extensor apparatus outward . This proximal release is then reduced  with a simple proximal horizontal transection of the rectus femoris tendon, then finally a diagonal section upward and outward of this tendon, which can continue in the fibers of the vastus lateralis muscle in a quadriceps snip. Della Valle et al.  and Barrack  agree that the usual anteromedial approach is sufficient in more than 90% of the cases and that the quadriceps snip is only rarely necessary. This has no incidence on rehabilitation and in the end the strength of the quadriceps is equal to that of the contralateral knee with prosthesis although less than the normal knee .
On the other hand, osteotomy of the anterior tibial tuberosity acts on the distal part of the extensor system. Its lateral levering widely frees the joint and facilitates arthrolysis. Modification of the position of the bone fragment aims to improve patellar position, in particular in terms of height, which proximal release does not provide.
Which bone block should be used? (variants and alternatives)
Instead of an osteotomy, Lyu  performed an osteomyofascial flap, sutured to the medial periosteum. He observed only one failure out of 22 caused by forced flexion during a fall with a final 10° active extension defect. However, is one certain to obtain a solid suture? A short bone fragment includes a risk of failure: those encountered by Wolff et al.  in 26 cases correspond to 3-cm bone fragments with a minimal contact surface and insufficient fixation [19, 20, 21, 22]. On the proximal side, we made a diagonal cut so as to raise the fragment. A step-cut tubercle osteotomy theoretically limits the risk of secondary displacement [5, 23], but none were observed in the present study. On the distal side, progressive joining [23, 24] weakens the tibia only minimally. A transversal osteotomy makes it possible to exert powerful mechanical distraction at the distal part of the fragment. However, osteotomy may lead to a second fracture of the tibia promoted by substantial osteoporosis , mobilization under anesthesia , a neurological problem such as charcot’s , or the extremity of an intramedullary stem at this level , a complication that we did not experience.
Since the initial description by Dolin  in 1983, Della Valle et al. , Hocking and Bourne , Laskin , Mendes et al. , Ries and Richman , Van den Broek et al. , and Whiteside  agree on the need for a sufficiently long bone fragment (>6cm) with several points that are sufficiently thick (>1 cm) so that the osteosynthesis does not weaken it (risk encountered in the series reported by Piedade et al. ), wide enough to provide a good contact surface to facilitate bone union.
The fixation mode
The fixation mode is debatable: Caldwell , Della Valle et al. , Hocking and Bourne , Laskin , Mendes et al. , and Whiteside  use two or three wire or metal cable cerclages around an intramedullary stem for better hold. Arnold et al. , Burki et al. , and Van den Broek et al.  prefer screws, as we do. The proximal triangular section of the tibia makes it possible to pass them in or out of an eventual stem. The mechanical studies conducted by Davis et al.  demonstrate the superiority of this type of fixation.
However, the overhang of the screw heads can become painful and require secondary ablation . The screws cannot be of the cancellous bone screw thread type (diameter, 6.5 mm): there would not be enough room between the cortical bone and the stem. Our practice has evolved toward a more sophisticated technology with resorbable screws with a flat head specifically designed for tubercle fixation. Their secondary resorption facilitates any ulterior revision.
The final position of the TT
The final position of the TT can be identical to the initial position: this is the simplification of the approach to a stiff knee  or this allows fixation or an allograft . The tibial tubercle can be medialized to assist treatment for patellar instability  and it can be raised or lowered to modify the height of the patella [21, 22]. In 19 cases of the present series, we raised the extensor apparatus a mean 13 mm (range, 8–33 mm). This raising is limited by the metallic tibial tray: a proximal process subjected to shearing can break when fatigued. Not having observed this principle, we encountered this complication, not yet reported in the literature, in two cases, with favorable progression following relative rest and no secondary migration of the fragment.
Translation of the TT is a little-used option in the literature reports [21, 22, 23, 24], with poorly specified indications. It is associated with a mean 15° gain in flexion (but this gain is multifactorial) and improvement in the patellar index, which has an incidence on the kinematics of the knee as soon as the level of the joint space varies .
Are there any contraindications to this TT osteotomy?
We have encountered no contraindications in our practice. In cases of major proximal tibial osteolysis, there would be no bone to heal to the TT. This contraindication is relative for Mendes et al. . Fragility of the skin (age, corticotherapy, scarring from earlier interventions) is a relative contraindication [20, 27]. The usual precautions, in particular the absence of subentaneous dissection, seems to have preserved our cases from extensive cutaneous necrosis.
Strengths, weakness, and originality of this study
This series is limited in the number of cases studied: 21 cases in 13 years, whereas Piedade et al.  described 126 cases in 7 years but only 18 anteromedial approaches. The other series range from 26 to 110 cases. We did not measure the strength of the extensor apparatus but clinically we observed no active extension defect. This is a retrospective and single-center study, like those in the literature. Translation of the TT is used most particularly in revisions (64 cases for Mendes et al. , 39 cases for Van den Broek et al. , 41 cases for Young et al. ), seldom in primary treatments (26 out of 136 for Whiteside , 18 medial approaches out of 126 for Piedade et al. , 11 out of 32 for Lavigne et al. ), and in our series in one-third of the cases. The literature reports few studies on patellar height [8, 31].
In surgery on difficult knees, during an anteromedial approach, osteotomy of the TT, even though it facilitates exposure in stiff knees, should not be considered simply as an approach. One should know how to use it to modify the patella position. It reduces risks of patellar tendon rupture. With careful technique, its fixation and its hold are reproducible. It contributes to improving knee function in cases of patella infera.
Disclosure of interest
The authors declare that they have no conflicts of interest concerning this article.