The Effects of Tibial Tuberosity-Trochlear Groove Distance on Lateral Translation of the Patella: A Cadaveric Biomechanical Study

Abstract

Background:

The tibial tuberosity-trochlear groove (TT-TG) distance is a key measurement in guiding surgical management of patellofemoral instability. A TT-TG of 20 mm is often used as the threshold for supplementing soft tissue procedures with tuberosity medialization, although this remains an active area of investigation.

Purpose:

To identify the relationship between TT-TG distance and the force required to cause lateral translation of the patella in a cadaveric model at 30º of flexion.

Study Design:

Descriptive laboratory study.

Methods:

Eight fresh-frozen human cadaveric knee specimens were acquired, and computed tomography scans were obtained to measure anatomic features of patellar instability. A flat tibial tuberosity osteotomy was performed. Specimens were mounted on an Instron ElectroPuls E10000 in 30° of flexion. The force (N) required to produce 10 mm of lateral patellar translation over a 1-second interval was measured under the following tibial tuberosity translation conditions: (1) native; (2) predetermined translation (+5, 10, and 15 mm from native); and (3) predetermined TT-TG values (10 to 25 mm by 5 mm increments).

Results:

For TT-TG values ≤20 mm, there was a significant negative linear relationship between the TT-TG distance and the force required for lateral patellar translation (–1.63 N/mm [95% CI, –1.637 to −1.629]; P < .001); 1 mm of TT-TG increase resulted in a 1.63 N decrease in the required force. With TT-TG testing conditions >20 mm, this linear relationship was no longer present (slope, –0.5 N/mm [95% CI, –1.36 to 0.36]; P = 0.25).

Conclusion:

The force required to translate the patella laterally decreased linearly as the TT-TG distance increased up to 20 mm. However, for TT-TG distances >20 mm, our model showed variability in the relationship between force and TT-TG distance.

Clinical Relevance:

The linear relationship identified between translational force and anatomic alignment, with TT-TG distances <20 mm, suggests a predictable biomechanical response to tibial tuberosity translation. The disruption of this relationship >20 mm confirms a threshold at which patellofemoral biomechanics are altered.

Keywords

biomechanics medial patellofemoral ligament patellofemoral instability tibial tuberosity osteotomy

Patellar instability is a relatively common pathology treated by orthopaedic surgeons, with lateral patellar subluxation or dislocation accounting for approximately 3% of all knee injuries, producing an annual incidence ranging from^11,43 5.8 to 43 per 100,000. First-time patellar instability events are often successfully managed nonsurgically.²² However, recurrent instability occurs in approximately 30% to 50% of patients managed nonoperatively.^4,18,29 As such, surgical intervention is frequently considered in the setting of recurrent instability, displaced osteochondral injury, or a first-time dislocator with a high-risk profile for recurrence.²²

During surgical planning, several essential soft tissue and bony features of the patellofemoral joint must be considered to optimize surgical outcomes. The status of the medial patellofemoral ligament (MPFL), which is the primary soft tissue restraint to lateral displacement of the patella from 0º to 30º of knee flexion, should be evaluated closely, as it is essential to address during stabilization surgery.²⁶ MPFL reconstruction has been established as the mainstay of treatment for MPFL rupture with recurrent instability. This procedure may be combined with bony procedures to address additional causes of patellofemoral maltracking.⁴³ Anatomic features that may contribute to patellar instability include patella alta, trochlear dysplasia, rotational abnormalities, and increased tibial tuberosity-tibial groove (TT-TG) distance.^1,20 Given the physical, psychological, and economic burden associated with managing patellar instability, defining the appropriate surgical indications remains a topic of great interest to surgeons and patients alike.^21,25,32

A normal TT-TG distance is considered 15 mm, as TT-TG distances >15 mm have been associated with an increased risk of recurrent instability.^35,39 Previous biomechanical studies have demonstrated that as the TT-TG distance increases, the extensor mechanism's laterally directed force vector on the patella is amplified and may ultimately exceed the bony and soft tissue constraints that maintain the patella within the trochlear groove during early knee flexion.^12,33,36 As such, in patients with recurrent lateral patellar instability and increased TT-TG distance, an MPFL reconstruction may be combined with a tibial tuberosity osteotomy (TTO) to reduce the TT-TG distance and improve patellofemoral tracking.³⁹ However, while a TT-TG distance of 20 mm has been commonly viewed as an indication for supplementing an MPFL reconstruction with a TTO, this remains an active area of both biomechanical and clinical investigation—it is still unclear as to which patients will benefit from MPFL reconstruction combined with a TTO.^{17,19,23,31,33,35}

Because of the complexity and potential complications of TTO in patellar stabilization surgery, a thorough understanding of the biomechanical impact of TT-TG modifying procedures is essential to mitigate risks and enhance patient outcomes.²⁷ There is currently a paucity of biomechanical evidence to support a specific TT-TG threshold, which necessitates a TTO in conjunction with an MPFL reconstruction. Therefore, the purpose of the following study is to use a cadaveric biomechanical model to elucidate the relationship between the TT-TG distance and the force required to produce lateral translation of the patella. This information can provide surgeons with a biomechanical rationale for performing a TTO in addition to MPFL reconstruction. This study hypothesized that the force required to translate the patella laterally would be negatively correlated with increasing TT-TG distance.

Methods

Institutional review board approval was not required for this cadaveric study, and all research was conducted in accordance with our institution's ethical guidelines. Biomechanical testing was performed in general accordance with the methods described by Vinod et al.⁴¹ A total of 8 fresh-frozen, human cadaveric knee specimens were used, consistent with sample sizes reported in comparable biomechanical investigations.^33,41 Donors were procured from an American Association of Tissue Banks-accredited whole body donation organization (Science Care). Donors with a history of knee surgery or degenerative joint disease were excluded from this study. Computed tomography (CT) scans were acquired using a SOMATOM Emotion 16 (Siemens AG) to measure TT-TG and sulcus angle to assess trochlear morphology. Patellar height, as well as coronal and rotational alignment, were not calculated because the provided specimens included only tissue from the distal thigh to the proximal leg. Degenerative changes were also absent in donor specimens, as reviewed on multiplanar CT scans. One measurement for each variable was performed by a single orthopedic surgeon (M.J.K.) using previously described techniques with the tools available in OsiriX Dicom Viewer 14 (Pixmeo SARL).^2,3,9,45 Once harvested, specimens were maintained in a freezer at −20 °C until approximately 24 hours before testing, then thawed to room temperature. Freeze-thaw cycles were minimized, and preparation and testing of all specimens were completed in ≤2 thaw cycles.

Specimen Preparation

Careful specimen preparation—including dissection with maintenance of the soft tissue constraints of the patellofemoral joint—was performed by a single orthopedic surgeon (M.J.K). In contrast to Vinod et al,⁴¹ the fibula was removed to facilitate mounting of the specimen in the testing apparatus. To create a reference point of the native tuberosity position before osteotomy, a 2.0-mm Kirschner wire (K-wire) was placed in a bicortical fashion perpendicular to the longitudinal tibial axis at the most prominent anterior point of the tibial tuberosity. The K-wire was removed, and a custom 3-dimensional (3D)-printed cutting jig was applied to perform a reproducible flat TTO parallel to the knee joint line and in plane with the posterior femoral condylar axis. A recessed cut was made in the osteotomy bed through the cutting jig to precisely accommodate placement of a 200 mm, ¼”-20 hole extended cheese plate mounting platform (CAMVATE Co) while also allowing the tibial tuberosity piece to sit flush with the cut surface of the tibia (Figure 1).

Figure 1.

Specimen preparation. (A) A dissected specimen with the fibula removed, mounted in a custom clamp apparatus with application of a 3D printed cutting jig held in place with 2 large K-wires placed parallel to the joint line in the plane of the posterior condylar axis. A blue nylon strap has been sutured to the residual quadriceps tendon. (B) Oblique view after application of cheese plates, demonstrating a flush relationship to the bone and tuberosity in the native position. (C) Lateral view showing the same features of panel B. (D) 3D rendering of a custom cutting jig allowing for a flat tuberosity osteotomy and a co-planar recessed cut for precise cheese plate application. 3D, 3-dimensional.

The free tuberosity piece was affixed to a second, 155 mm, ¼” 20-hole standard cheese plate mounting platform. The 2 cheese plates were secured to the specimen in a parallel, planar fashion, with their central slots aligned, thereby allowing stable and reproducible direct medial-lateral translation of the tibial tuberosity across a continuous spectrum of predetermined tuberosity translation distances and TT-TG values (Figure 2 and Figure 4).

Figure 2.

Cheese plate functionality. The tuberosity piece is fixed to a secondary cheese plate. Through non-threaded, aligned channels in the 2 plates, a pair of nuts and bolts stabilizes the tuberosity at any medial/lateral translation point. (A) Lateral tuberosity translation. (B) Native tuberosity position. (C) Medial tuberosity translation.

A rigid metal eyelet was threaded into the lateral border of the patella at the junction of the middle and proximal thirds in plane with the posterior condylar axis. This form of rigid fixation was selected to ensure consistent fixation with reduced concern for laxity within the testing system. This differed from the work above by Vinod et al,⁴¹ which used soft tissue suture fixation. A 1-inch-wide nylon strap was sewn to the residual quadriceps tendon in a Krakow fashion with a No. 5 FiberWire suture (Arthrex Inc) to allow maintenance of tension in the extensor mechanism during testing.

Experimental Testing

Lateral patellar translation force was performed and recorded by an Instron ElectroPuls E10000 Linear-Torsion Testing System (Instron Corp).⁴¹ Specimens were rigidly secured to the base of the load frame using custom fixtures. Each bracket contained colinear guide holes for two 5.0-mm transfixion pins to be passed through the femoral and tibial segments, preventing specimen translation or rotation during testing. The specimens were positioned in neutral knee joint rotation at 30º of flexion, the position at which the patella engages the trochlea. Positioning was verified by a goniometer and a level. Specimens were positioned such that the lateral aspect of the patella was in line with and attached to the actuator of the load frame via a rigid S-hook placed through the metal eyelet (Figure 3).

Figure 3.

Experimental setup. The specimen is mounted within the materials testing device in 30º of flexion. An eyelet and S-hook rigidly fasten the patella to the actuator. Tension in the extensor mechanism is maintained via a 20 kg kettlebell (not pictured) hanging from a nylon strap affixed to the quadriceps tendon, routed over a pulley. No translation or rotation of the femur or tibia was permitted.

Figure 4.

Demonstration of the medial-lateral translation function of the cheese plate with the specimen mounted in the testing apparatus. (A) Lateral translation. (B) Medial translation. The hole in the osteotomy bed in panel B serves as the K-wire reference pathway for the native tuberosity position, corresponding to the hole in the tuberosity piece located in the central slot of the small cheese plate.

Tension was applied to the extensor mechanism via the nylon strap by attaching a 20 kg weight and hanging it over a pulley. The patella was then laterally translated 1 cm at a rate of 10 mm/sec in the following tibial tuberosity translation conditions in a computerized random order: native, ± 5 mm from native, ± 10 mm from native, ± 15 mm from native, TT-TG = 10 mm, TT-TG = 15 mm, TT-TG = 20 mm, and TT-TG = 25 mm. No loosening or fixation loss was observed during testing.

Native positioning was achieved by replacing the K-wire in the previously created bicortical pathway before performing the osteotomy. Translation was performed using a digital caliper from native positioning.³³ Force (N) and displacement (mm) data were collected digitally by the ElectroPuls software, and peak force from each cycle was recorded. Three trials were performed for each condition and averaged for analysis.

Statistical analysis

Data were analyzed using SAS, Version 9.4 (SAS Institute Inc). Generalized estimating equations were used to assess how the peak force required to translate the patella 1 cm changed across testing conditions, accounting for repeated measures within each specimen. This approach allowed inclusion of specimens with missing data and addressed within-specimen correlations. Pairwise comparisons between conditions were performed, with the Holm method used to adjust for multiple comparisons and maintain an overall alpha of .05. The marginal slope from the linear regression model, reflecting the change in force (N) per mm change in tuberosity position for each specimen, is reported along with the corresponding 95% CI and P value. P < .05 was selected to represent statistical significance.

Results

Eight fresh-frozen knee specimens were included in this study (5 women; mean age, 71.3 ± 6.5 years). Imaging and direct visualization showed no evidence of patellofemoral osteoarthritis in any specimen. One specimen exhibited a sulcus angle indicative of borderline trochlear dysplasia (Specimen No. 3; sulcus angle = 145), and 1 specimen had an elevated native TT-TG (Specimen No. 8; TT-TG = 20 mm) (Table 1).

Table 1

Specimen Characteristics and CT Measurements ^a

Specimen Number	Age	Sex	Height, cm	Weight, kg	TT-TG, mm	Sulcus angle, deg
1	60	F	163	62.6	8	135
2	72	M	178	68.9	12	133
3	73	F	157	54.9	11	145
4	73	F	155	61.2	5	136
5	79	F	168	101.2	9	120
6	66	F	160	81.6	9	140
7	68	M	183	84.4	13	138
8	79	M	168	42.2	20	130

CT, computed tomography; F, female; M, male; TT-TG, tibial tuberosity-trochlear groove.

The results for all testing conditions and trials for each specimen are reported in Supplemental Table 1. For testing conditions in which TT-TG values ≤20 mm, there was a strong, negative linear relationship between the TT-TG distance and force required for translation (slope, –1.63 [95% CI, –1.637 to −1.629]; P < .001). For each mm of lateral TT-TG translation, 1.63 N less force was required to translate the patella laterally (Table 2).

Table 2

Summary of Linear Regression Model Separated by All TT-TG Values and TT-TG Values <20 mm ^a

Specimen Number	Linear Regression, TT-TGs <20 mm			Linear Regression, All TT-TGs Tested
Specimen Number	Slope	95% CI	P	Slope	95% CI	P
1	−1.11	–1.24 to −0.98	<.0001	−0.41	−0.44 to −0.37	<.0001
2	−2.48	−2.63 to −2.34	<.0001	−1.41	−1.53 to −1.28	<.0001
3	−1.01	−1.09 to −0.92	<.0001	−0.66	−0.72 to −0.61	<.0001
4	−1.74	−1.85 to −1.64	<.0001	−1.55	−1.62 to −1.48	<.0001
5	−1.46	−1.52 to −1.40	<.0001	−0.47	−0.48 to −0.45	<.0001
6	−2.31	−2.38 to −2.24	<.0001	1.74	1.63 to 1.85	<.0001
7	−1.2	−1.23 to −1.18	<.0001	1.1	1.04 to 1.16	<.0001
8	−1.98	−2.06 to −1.90	<.0001	−2.3	−2.44 to −2.17	<.0001
Overall	−1.63	−1.637 to −1.629	<.0001	−0.5	−1.36 to 0.36	0.25

TT-TG, tibial tuberosity-trochlear groove.

With TT-TG testing conditions >20 mm, this linear relationship is disrupted by significant variability in force behavior and does not achieve statistical significance (slope, –0.5 [95% CI, –1.36 to 0.36]; P = .25). In 6 of 8 specimens, an opposite relationship of increased force was observed with continued lateral translation beyond a TT-TG distance of 20 mm, whereas 2 of 8 specimens continued to show a negative (Figure 5).

Figure 5.

Graph representing force required to achieve 1 cm of lateral patellar translation for all measured TT-TG values for all tested specimens. The linear relationship for TT-TG values <20 mm is represented by a simple line of best fit, independent of the regression modeling for each specimen. TT-TG, tibial tuberosity-trochlear groove.

Discussion

The primary objective was to identify the relationship between TT-TG distance and the force required to produce lateral translation of the patella in a cadaveric model. For TT-TG distances <20 mm, our hypothesis was confirmed: there was a strong negative linear relationship between increasing TT-TG distance and the force required to translate the patella laterally by 1 cm. However, for TT-TG values >20 mm, this relationship showed substantial variation in force behavior, with 6 of 8 specimens exhibiting increased required force, whereas 2 continued to show a negative relationship. These findings provide a more comprehensive understanding of the relationship between tibial tuberosity position and the risk of lateral patellar instability and underscore the importance of including TT-TG distance as one of many objective measures in the evaluation of patients with recurrent instability.

The strong linear correlation between force and patellar translation observed in our study for TT-TG distances <20 mm aligns with the established literature and supports the role of both bony and soft tissue constraints in maintaining normal physiologic patellar tracking.^13,33,36 The negative linear slope indicates that for each millimeter of tuberosity lateralization, 1.63 N less force is required to produce 1 mm of lateral patellar translation. This suggests that each millimeter of tuberosity medialization provides a protective effect of 1.63 N against lateral patellar displacement within this TT-TG range. By identifying the linear relationship between translational force and anatomic alignment, this study provides a potential foundation for developing an individualized surgical planning framework. This may aid in determining the degree of medialization needed to achieve stability while avoiding overcorrection, which can inadvertently elevate medial patellofemoral contact pressures and cause iatrogenic complications. Thus, this finding supports a balanced approach—optimizing correction not only to enhance lateral stability, but also to preserve joint congruity and minimize abnormal contact forces.^6,37,38,44

The results of the present work support the longstanding precedent established by Dejour et al¹³ that patellar dislocation is highly associated with elevated TT-TG distances, indicating that surgical treatment in symptomatic patients with this extensor mechanism geometry should include bony realignment procedures. Amidst mixed clinical and biomechanical results regarding the accuracy of 20 mm as a true cutoff for the need to implement a bony procedure in the surgical management of this patellofemoral instability,^‖ the present study contributes further nuance to the biomechanical phenomenon popularized by Dejour.¹³

Notably, as TT-TG distances exceeded 20 mm in this study, the previously observed linear relationship was lost, with only 2 of the 8 specimens showing a continued negative trend and the remaining 6 demonstrating an inversion of this relationship. The observed increase in force under testing conditions with TT-TG distances >20 mm may result from the induced tuberosity translation causing forceful engagement of the patella against the lateral wall of the trochlea at time zero, before any laterally directed force is applied. In this setting, when the lateral patellar force is applied, resistance may be increased due to greater initial lateral trochlear containment and simultaneous increased pretensioning of soft tissue restraints. Restriction of tibial rotation within the mounting fixtures may also have contributed to this observation. Increased force with TT-TG distances >20 mm was the more frequent finding in the present study (6/8 specimens), and is congruent with previous biomechanical studies demonstrating the stabilizing effects of the medial and lateral retinacular structures against lateral patellar translation.^8,10,14,28

While biomechanics of the patellofemoral joint have been widely studied, the force required to cause lateral patellar translation represents another avenue in improving the understanding of this multifaceted joint. Vinod et al⁴¹ demonstrated the effects of a trochlear flattening osteotomy on the force required to cause lateral patellar translation in the context of various states of MPFL integrity and knee flexion angles. This work inspired the testing setup for the present study; however, despite similar methods, our measured forces were notably greater (~50-230 N) than those of the comparison study (~40-60 N) at 30º of knee flexion (Figure 5). While different variables were studied in these 2 works, this difference highlights the influence of factors such as specimen characteristics, biomechanical testing setups, soft tissue integrity, and experimental constraints on the biomechanical evaluation of patellar instability, underscoring the need for standardization in experimental methodology. Our current work sought to create reproducibility in testing within each specimen by applying the photography mounting cheese plates for tuberosity translation. This novel technique affords easily measured, reproducible, and rigid tuberosity fixation throughout a continuous spectrum of TT-TG values and may be applied in further investigation.

Limitations

This study has several noteworthy limitations. One primary limitation is the use of cadaveric specimens, which come with inherent limitations. The age and cartilage condition of the specimens were not representative of the target population, as patellofemoral instability is most commonly identified in adolescents. Additionally, the history of knee pain or instability among the donors could not be ascertained; however, we reviewed the background report for each specimen and identified no exclusions. Radiographic measurements and specimen preparation, including osteotomies, were performed by a single orthopedic surgeon, introducing the potential for human error; however, any error would have been applied uniformly across all specimens. Moreover, the measurement technique used for TT-TG has demonstrated excellent reliability, with an interrater intraclass correlation coefficient of 0.97, and all osteotomies were performed using a fixed cutting jig to ensure consistency.³

Although freeze-thaw cycles were minimized and all specimens were tested within 2 thawing events, this cycling may still introduce variability in tissue quality and testing results. The specimens consisted only of a knee, sectioned at the mid/distal femur and the middle third of the tibia, which limited a true assessment of native morphological features such as patella alta or rotational deformities. Furthermore, the study was conducted exclusively at 30º of knee flexion, selected because this is the position at which the patella engages the trochlea. However, this does not account for the full range of patellofemoral engagement throughout an arc of motion, thereby precluding any inferences about anisometry of the medial soft tissue restraints. Additionally, the preservation of periarticular soft tissues in the experimental design precluded direct determination of the patella's initial position within the trochlear groove for each TT-TG testing condition. This also may have led to unintentional pretensioning of the medial restraints, particularly with high TT-TG distances (>20 mm). Moreover, the restriction of tibial rotation may have further altered native patellofemoral mechanics under these conditions and contributed to the loss of linearity observed at higher TT-TG conditions.

Conclusion

The present study found that the force required to translate the patella laterally at 30º of knee flexion decreased linearly as the TT-TG distance increased up to 20 mm. However, for >20 mm, our model demonstrated significant variability in the force-to-TT-TG relationship.

Footnotes

Final revision submitted October 21, 2025; accepted November 28, 2025.

One or more of the authors has declared the following potential conflict of interest or source of funding: M.J.K. has received hospitality payments from Zimmer Biomet. M.A.B. has received hospitality payments from Zimmer Biomet and Stryker Corporation. B.D.O. receives royalties/licensing fees and provides consulting services for Linvatec Corporation. B.D.O. also serves as a consultant for DePuy Synthes Products, Inc, Vericel Corporation, and Medical Device Business Services, Inc. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Ethical approval was not sought for the present study.

ORCID iDs

Michael J. Kutschke

Edward J. Testa

Matthew S. Quinn

Michael A. Bergen

Supplemental Material

Supplemental Material for this article is available at .

Notes

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