Interrelations Between the Too-Long Anterior Calcaneal Process, Hind and Mid-tarsal Bone Volumes, Angles and Osteochondral Lesion of the Dome of the Talus: Analysis by Software Slicer of 69 CT Scan of Feet

Abstract

Introduction

Although the association between Too-Long Anterior Calcaneal Process (TLACP) and osteochondral lesion of the dome of the talus (OCL) has been hypothesized, no study has investigated the interrelations between TLACP, hind and mid-tarsal volumes and angles and the development of OCL. The main goals of this work are: (1) to measure the volume of the calcaneum, talus, navicular and cuboid in subjects with and without TLACP; (2) to evaluate the angular relationships between talus, calcaneum and navicular in subjects with and without TLACP; (3) to assess whether TLACP has an effect on the volume of OCL.

Methods

This is a retrospective study of 69 CT scans of 54 consecutive children aged 11–15 years who had undergone a CT scan due to symptomatology suggestive of TLACP. The 3D Slicer software allowed to calculate the volume of the talus, calcaneum, navicular, cuboid, TLACP and OCL (in cm³). The PACS system was used to perform the angular measurements (in degrees) between talus, calcaneum and navicular in the frontal, axial and sagittal plane.

Results

Amid the 69 CT scans, 49 were found to have pathologies related to TLACP (71%, TLACP Group) and 20/69 were normal (29%, Control Group). The mean hind and mid-tarsal bone volumes of the TLACP group were comparable to those of the control group. There were 40 (81.6%) OCLs detected exclusively in pathological feet (TLACP group); 32 lesions were medial (80%), and 8 lesions were lateral (20%). According to Ferkel and Sgaglione CT Staging System, there were 22 (55%) stage 1 lesions, 5 (12.5%) stage 2A, 3 (7.5%) stage 2B and 10 (25%) stage three lesions. Only the angle between the talus and calcaneum in the frontal plane was significantly lower in pathological feet with respect to the control group (p < 0.001). In pathological feet, the talus was supinated, and the calcaneus pronated.

Conclusions

TLACP tend to stiffen the foot, modifying its biomechanics and leading to supination of the talus and pronation of the calcaneum. This induces an overpressure at the medial side of the talus where we observed a greater frequency of medial OCL with larger volume than lateral OCL.

Level of Evidence

III

Introduction

The Too-Long Anterior Calcaneal Process (TLACP) corresponds to an elongated extension of the anterior portion of the calcaneum similar to the nose of an anteater. It is an insufficient or terminated tarsal coalition between the calcaneum and the navicular bone [1–4] and it can be the source of calcaneo-navicular impingement when the distance between the two bones is less than 5 mm [1, 3, 5]. Clinical symptoms of TLACP are hind and mid-tarsal pain on supination, forefoot stiffness with decreased inversion, eversion and plantar flexion, and recurrent sprains [5–7]. Although the association between TLACP and osteochondral lesion of the dome of the talus (OCL) has been hypothesized [8], no study has investigated the interrelations between TLACP, hind and mid-tarsal volumes and angles and the development of OCL. Thus far, it has been reported by several authors that the stiffness of the foot, secondary to TLACP, can be associated with mechanical overload at the level of nearby joints and it can be involved in the development of OCL [9, 10]. This phenomenon, called the “nutcraking effect”, is due to the biomechanical imbalance induced by the presence of TLACP, causing a hyper pressure at the tibio-talar joint resulting in micro-fractures, localized necrosis, and geodes at the level of the dome of the talus. The more recurrent medial OCL are believed to be the outcome of a squeezing mechanism of the talus by plantar flexion of the foot and supination [9], while lateral lesions are believed to be an indirect outcome of a trimming mechanism with the foot in dorsal flexion and pronation [10–12]. However, there is a lack of data concerning the volumes and the spatial relationship of hind and mid-tarsal bones, as well as their relationship with OCL, when the diagnosis of TLACP is confirmed [11–15].

The main objective of our work was: (1) to measure the volume of the calcaneum, talus, navicular and cuboid in subjects with and without TLACP; (2) to evaluate the angular relationships between talus and calcaneum, talus and navicular, calcaneum and navicular in the frontal, axial and sagittal plane in subjects with and without TLACP; (3) calculate the volume (size) of OCLs in the TLACP group and in the control group.

The hypothesis is that TLACP stiffens the foot, and leads to supination of the talus and pronation of the calcaneum, thus increasing the occurrence of OCD lesions where the pressure is higher (medial versus lateral side of the talus).

Materials and Methods

This is a retrospective study of 69 CT scans of 54 consecutive children. After having received the Institutional Review Board approval, we examined data from patients who obtained an ankle or foot CT scan between January 2011 and January 2020. The study included children aged 11–15 years who had undergone a CT scan due to the demonstration of a symptomatology suggestive of TLACP (frequent sprains, pronation pain, tarsal stiffness). This study did not include patients who had a CT scan but who had a history of foot or ankle surgery not caused by OCL or TLACP. We also excluded patients with syndromes who were unable to walk and patients with foot problems but associated with pre-existing neurological conditions.

All the CT scans measurements were performed by a pediatric orthopedic surgical resident (GL) and a senior pediatric orthopedic surgeon (FC); the two examiners searched for TLACP and/or OCL on the CT scan and were unrelated to clinical diagnosis and treatment of the cases studied. Amid the 69 CT scans, 49 were found to have pathologies related to TLACP (71%, TLACP Group) and 20/69 were normal (29%, Control Group); the normal feet are those of patients where the TLACP was suspected, but a subsequent CT scan resulted in a negative TLACP diagnosis. At the time of the CT scans, only the age and gender of the patients were known to preserve patient anonymity, and these scans were used to identify patients with normal and abnormal feet.

• In particular, CT scan images were used to perform the following:

  • (I)
    The calculation of the distance in millimeters (mm) from the distal end of the anteromedial process of the calcaneum to the navicular bone in multiplanar reconstruction on sagittal sections along a perpendicular axis to this line in the axial section. The diagnosis of TLACP was determined by a calcaneo-navicular (CN) distance of less than 4 mm (Fig. 1) [16]. All radiographic measurements were performed on the PACS System (Philips Medical Systems, Best, Netherland
  • (II)
    The use of 3D Slicer software (Version 4.11, www.slicer.org) [17] allowed for the direct input of the CT scans and those images were used to segment and calculate (Fig. 2)

    • A.
      The volume of the talus, calcaneum, navicular and cuboid (in cm³)
    • B.
      The volume of the TLACP in (in cm³)
    • C.
      The location (lateral or medial) and volume (in cm³) of OCL, when present
    • D.
      The stage of OCL according to the Ferkel and Sgaglione CT Staging System [18]
  • (III)
    The PACS system (Philips Medical Systems, Best, The Netherlands) was used to perform the following angular measurements (all expressed in degrees)

    • A.
      The angle between the main axis of calcaneum and the main axis of talus in the axial (αCTa), frontal (αCTf) and sagittal (αCTs) plane (Fig. 3)
    • B.
      The angle between the main axis of calcaneum and the main axis of navicular in the axial (αCNa) and sagittal (αCNs) plane (Fig. 4)
    • C.
      The angle between the main axis of talus and the main axis of navicular in the axial (αTNa) and sagittal (αTNs) plane (Fig. 5)

Fig. 1.

Schematic representation of the TLACP. d calcaneo-navicular distance, N navicular, Cu cuboid, Ta talus, C calcaneus

Fig. 2.

Segmentation of the volumes of the tarsal bones and the TLACP with slicer software

Fig. 3.

αCTf/αCTa/αCTs the angle between the main axis of calcaneum and the main axis of talus in the frontal (αCTf), in the axial (αCTa) and sagittal (αCTs) projection

Fig. 4.

αCNa/αCNs the angle between the main axis of calcaneum and the main axis of navicular in the axial (αCNa) and sagittal (αCNs) projection

Fig. 5.

αTNa/αTNs the angle between the main axis of talus and the main axis of navicular in the axial (αTNa) and sagittal (αTNs) projection

Statistical Analysis

Stata software, version 13 (StataCorp, College Station, TX, US) was used to conduct a statistical analysis where quantitative data were conveyed as means and ranges. A student’s t test, using quantitative parameters and a statistical significance set to a p value < 0.05, was performed to compare the averages of the observed characteristics relative to the presence of pathologies and those associated with specific pathologies. The intra- and inter-observer agreement was determined by performing weighted Kappa coefficient calculation.

Result

Demographic of Patients

This study examined 69 feet of 54 patients (20 males and 34 females) aged 11 to 15 years (mean age: 13 ± 2 years). The mean age of the patients in the TLACP group was 13.3 ± 2.1 years and was similar to that of the patients in the control group (12.5 ± 1.8 years; p > 0.05 (Table 1).

Table 1.

Demographic characteristics of patients

	Total	Normal (control group)	Pathological (TLACP group)	p value
Number of feet [patients]	69 [54]	20 (29%)	49 (71%)	N/A
Age (years)	13 ± 2	12.5 ± 1.8	13.3 ± 2.1	> 0.05
M:F (feet)	30:39	9:11	21:28	> 0.05
Left:right (feet)	32:37	11:9	21:28	> 0.05

TLACP too long anterior calcaneal process

Calcaneo-Navicular Distance

There were 20 out of 69 feet (29%) that showed no abnormalities of the anterior calcaneum process, and these were used as the control group. Among normal feet, the mean CN distance was 10.3 ± 1.6 mm. A total of 49 out of 69 feet (71%) showed the presence of a TLACP (TLACP group), which was confirmed by significantly reduced CN distance (2.8 ± 1.2; p < 0.001) compared to the feet present in the control group (Table 2).

Table 2.

Linear and volumetric measurements

	Total	Normal (control group)	Pathological (TLACP group)	p value
Number of feet	69	20	49	N/A
L bone (t) CCu (mm)	8 ± 4.5	1.4 ± 0.6*	10.7 ± 1.9*	< 0.001*
Distance CN (mm)	5 ± 3.7	10.3 ± 1.6*	2.8 ± 1.2*	< 0.001*
Calcanear volume (cm3)	51.3 ± 7.1	51.2 ± 7.6	51.3 ± 7	> 0.05
TLACP volume (cm3)	N/A	N/A	1.1 ± 0.7	N/A
TALUS volume (cm3)	32.2 ± 4.4	31.2 ± 4.1	32.7 ± 4.5	> 0.05
Navicular volume (cm3)	10.4 ± 2.3	11.2 ± 2	10 ± 2.3	> 0.05
Cuboid volume (cm3)	9.4 ± 1.6	9.8 ± 1.9	9.3 ± 1.5	> 0.05
OCL volume (cm3)	0.5 ± 0.3	N/A	0.5 ± 0.3	> 0.05

L Bone (t) CCu length of bone distal to the tangent of calcaneocuboid joint, distance CN calcaneo-navicular distance. OCL osteochondral lesion of the dome of the talus. TLACP too long anterior calcaneal process

Data where there is statistical significance are in bold

The data in which statistical calculations have given significance are with the symbol (*)

Volumes

• A.Volume of talus, calcaneus, navicular, cuboid

The mean hind and mid-tarsal bone volumes of the TLACP group were comparable to those of the control group. Table 2 summarizes the volumes of normal and pathological feet

• B.Volume of TLACP

The mean volumes of the TLACP group were 1.1 ± 0.7 cm³ (Table 2); it is important to note that the volume of calcaneum did not differ significantly between groups when the volume of TLACP was excluded from the analysis.

Angles

Table 3 summarizes angular measurements in both normal (control group) and pathological feet (TLACP group). Sagittal (αCNs, αTCs, αTNs) and axial (αCNa, αTCa, αTNa) measurements in patients with TLACP were similar to those of the control group (p > 0.05). On the other hand, the angle between the talus and calcaneum in the frontal plane (αCTf) was significantly lower with respect to the control group (p < 0.001). In pathological feet, the talus was supinated and the calcaneum pronated (Fig. 6). This spatial orientation can cause an overload on the medial side of the talus leading to a higher number of medial OCL with a larger volume compared to the lateral OCL (Table 4); in addition, no OCL were detected in normal feet.

Table 3.

Angular measurements in degrees

	Total	Normal (control group)	Pathological (TLACP group)	p value
αCTf	27.4 ± 11	12.1 ± 5.0*	33.8 ± 4.5*	< 0.001*
αCTa	23.8 ± 4.1	22.1 ± 2.7	24.5 ± 4.4	> 0.05
αCTs	19.1 ± 3.2	18.9 ± 2.6	19.1 ± 3.5	> 0.05
αCNa	1 ± 0.1	3.2 ± 2	5.3 ± 3.8	> 0.05
αCNs	39.1 ± 7.9	38.1 ± 6.7	39.5 ± 8.4	> 0.05
αTNa	32.8 ± 7.5	32.6 ± 6.7	32.9 ± 7.9	> 0.05
αTNs	6 ± 1.2	5.5 ± 2.1	6.4 ± 2.9	> 0.05

Data where there is statistical significance are in bold

The data in which statistical calculations have given significance are with the symbol (*)

Fig. 6.

Schematic representation of the tibia-talar mechanical overload mechanism that causes osteochondral lesions of the talus

Table 4.

Radiological characteristics of OCL in patients with TLACP (n = 49) according to the Ferkel and Sgaglione CT staging system

	Total number	Stage 1	Stage 2A	Stage 2B	Stage 3	Stage 4	p value
Number of OCL	40/49 TLAP (81.6%)	22 (55%)	5 (12.5%)	3 (7.5%)	10 (25%)	0 (0%)	N/A
Medial location	32 (80%)	16 (50%)	4 (12.5%)	2 (6.3%)	10 (31.2%)	0 (0%)	< 0.001
Lateral location	8 (20%)	6 (75%)	1 (12.5%)	0(0%)	1 (12.5%)	0 (0%)	< 0.001
Volume (cm3)	0.5 ± 0.3(M 0.5 ± 0.3/L 0.1 ± 0.1)	0.3 ± 0.2	0.5 ± 0.4	0.6 ± 0.2	0.8 ± 0.3	N/A	< 0.001

OCL osteochondral lesion of the dome of the talus. TLACP too long anterior calcaneal process. M medial OCL. L lateral OCL

Data where there is statistical significance are in bold

Volume and Staging of OCL

There were 40 (81.6%) OCLs detected exclusively in pathological feet (TLACP group); 32 lesions were medial (80%), and 8 lesions were lateral (20%). According to Ferkel and Sgaglione CT Staging System, [18] there were 22 (55%) stage 1 lesions, 5 (12.5%) stage 2A, 3 (7.5%) stage 2B and 10 (25%) stage 3 lesions. A medial OCL had a larger volume (0.5 ± 0.3) than a lateral OCL (0.1 ± 0.1; p < 0.001).

In all parameters, there was an excellent intra- and inter-observer agreement with weighted Kappa coefficients of 0.812 and 0.842, respectively.

Discussion

The present study investigated the relationship between volumes and angles of the hind and mid-tarsal bones and the occurrence of OCL in patients with and without TLACP. The analysis of our results shows volumes of pathological and normal feet are comparable. However, angle measurements revealed that the angle between the talus and calcaneum in the frontal plane is significantly lower in pathological (TLACP group) rather than in normal feet. In the TLACP group the talus is supinated and the calcaneum is pronated, thus potentially explaining the higher number of medial OCL in feet with TLACP. The results of our work, which must still be regarded as preliminary, have as a possible clinical implication that early diagnosis and early treatment of TLACP may prevent the onset of OCL, especially on the medial side of the talus.

The mean hind and mid-tarsal bone volumes of the TLACP group were comparable to those of the control group highlighting the presence of TLACP does not alter the volumetric development of other hindfoot bones (Table 2). On the other hand, patients with TLACP had all angles, but αCTf, comparable to those of patients without TLACP (Table 3).

The study is the first to use software to calculate the volumes of the children's foot bones [10–12]. Furthermore, the analysis of all angular measurements allowed us to show how there is a biomechanical alteration of the tarsal bones in patients with TLACP (Fig. 7). The presence of a TLACP protruding between the talus, navicular, and cuboid could reduce the mobility of the hind and mid-tarsal bones and it contributes to the supination of the talus and pronation of the calcaneum. Carlson et al. reported that the talus shares the mechanical stresses between the calcaneum and the metatarsals, hence the presence of an anatomical defect, such as TLACP, can be considered as a cause of alteration in the biomechanics of the foot.

Fig. 7.

CT scan shows TLACP and OCL in the same patient. A sagittal view B frontal view

The resulting hind and mid-tarsal stiffness in feet TLACP positive may alter the biomechanics of the hindfoot leading to a mechanical weight on the ankle with medial hyper pressure further enhanced by the supination of the talus [8, 19–22]. There would be a modification of the force transmission pattern, causing excessive overload at the level of the ankle, specifically on the medial side (Fig. 6) [23–25]. In particular, among TLACP positive feet, 80% of the OCL were medial and only 20% were lateral.

It was difficult to avoid classification bias whilst finding a relevant control group within this study. A limitation is that the scans used constrained ankles with a 90° positioning, which could result in diverse CN distances while under load. Being that standardized technique of measuring TLACP in imaging was not found, we used CT scans to locate the smallest distance found within the anteromedial process of the calcaneum and the navicular in axial slices. Another predominant limitation of the study is the limited amount of feet found in the OCL group with a CN distance that is greater than 5 mm. This significantly decreases the strength of the analyses. Furthermore, the patients in this particular group were younger which implies that they had a foot that was not completely ossified. Appropriate diagnostic criteria for this condition have proven difficult, as definitions and radiological analyses seem to differ greatly when consulting the very numerous studies that exist. TLACP has been previously defined as a CN distance of less than 5 mm using CT scans, but the vast amount of patients in the control group with below average CN distance could pose an issue to this definition. The development of new imaging techniques could help define, with further precision, a threshold that would provide a more detailed definition of a condition originally outlined through radiographic images.

In conclusion, TLACP tend to stiffen the foot, modifying its biomechanics and leading to supination of the talus and pronation of the calcaneum. This induces an overpressure at the medial side of the talus where we observed a greater frequency of medial OCL with larger volume than lateral OCL. Despite our findings, more studies will be needed to fully understand the nature of TLACP and its correlation with the bones of the foot, and to determine whether early identification and resection of a TLACP can preserve the normal biomechanics of the foot and prevent the development of OCL.

Author contributions

Conceptualization: GL, FC. Data collection: GL, NM, FC. Data analysis: GL, FC, RS, FB. Writing of the manuscript: GL, FC, NO. Critical revision: FB, AD, NB.

Funding

The authors have no relevant financial or non-financial interests to disclose.

Data availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Declarations

Conflict of interest

None declared.

Ethical approval

All authors have given their final approval of the version to be published. Approval was granted by the Ethics Committee of University Lille (DEC21-178).